New Boiler to replace a old Worcester 35CDi II

j3oeff · Jan 16, 2022

John.g said:
Oh Yes, quite right, corrected now and important to get it as your tests show, actually makes a better case as the average boiler output is lower again, at 21.1kw.
As a matter of interest, you seem to have shut the bath tap in a bit? to get the temperature up for the last two tests but the (flow) times make no sense, do you have them?.

Bath tap
4.12 - 31.7c
4.27 - 34.6c
19.5 - 41.2c
25.6 - 41.4c

DHW
Boiler
Mains
Setpoint
Rated

Temp
Temp
Output

DegC
DegC
KW

12
60
30

Measured
Achievable
Required
Actual

Kitchen
Temp
Temp
Output
Output

LPM
DegC
DegC
KW
KW

5.6
47
60
18.6
13.6

5.6
43.5
60
18.8
12.4

5.7
42.9
60
19.0
12.3

5.8
42.3
60
19.4
12.3

5.7
43.9
60.0
19.0
12.6
Average

Downstairs

Bathroom
Measured
Achievable
Required
Actual

Tap
Temp
Temp
Output
Output

LPM
DegC
DegC
KW
KW

9.6
37.7
56.6
30.0
17.3

9.0
36.3
59.9
30.0
15.2

9.3
37.0
58.3
30.0
16.2
Average
Upstairs

Bathroom
Measured
Achievable
Required
Actual

Tap
Temp
Temp
Output
Output

LPM
DegC
DegC
KW
KW

10.1
35.0
54.7
30.0
16.2
11.1
34.9
50.7
30.0
17.8
10.6
35.0
52.7
30.0
17.0
Average
Ensuite
Sink
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
LPM
DegC
DegC
KW
KW
9.0
37.8
59.8
30.0
16.2
9.4
39.3
57.7
30.0
17.9
9.2
38.6
58.7
30.0
17.1
Average
Bath
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
LPM
DegC
DegC
KW
KW
14.6
31.7
41.5
30.0
20.0
14.1
34.6
42.6
30.0
22.2
14.3
33.2
42.1
30.0
21.1
Average

19.5 - 41.2c
25.6 - 41.4c

I did turn the tap off abit too see if it got any hotter. I still followed the same process which was 1 litre jug fills which took as above....19.5 seconds and 25.6 seconds resulting in those water temperatures within the jug.

John.g · Jan 16, 2022

This is the icing on the cake j3, (I was looking for 20kw or something like that) as it proves beyond all doubt that when one tap is throttled in, the boiler only produces ~ 60% of the required output even though very well within its rated output.

	DHW	Boiler
Mains	Setpoint	Rated
Temp	Temp	Output
DegC	DegC	KW
12	60	30
	Measured	Achievable	Required	Actual
Kitchen	Temp	Temp	Output	Output
LPM	DegC	DegC	KW	KW
5.6	47	60	18.6	13.6
5.6	43.5	60	18.8	12.4
5.7	42.9	60	19.0	12.3
5.8	42.3	60	19.4	12.3
5.7	43.9	60.0	19.0	12.6	Average
Downstairs
Bathroom	Measured	Achievable	Required	Actual
Tap	Temp	Temp	Output	Output
LPM	DegC	DegC	KW	KW
9.6	37.7	56.6	30.0	17.3
9.0	36.3	59.9	30.0	15.2
9.3	37.0	58.3	30.0	16.2	Average
Upstairs
Bathroom	Measured	Achievable	Required	Actual
Tap	Temp	Temp	Output	Output
LPM	DegC	DegC	KW	KW
10.1	35.0	54.7	30.0	16.2
11.1	34.9	50.7	30.0	17.8
10.6	35.0	52.7	30.0	17.0	Average
Ensuite
Sink	Measured	Achievable	Required	Actual
Tap	Temp	Temp	Output	Output
LPM	DegC	DegC	KW	KW
9.0	37.8	59.8	30.0	16.2
9.4	39.3	57.7	30.0	17.9
9.2	38.6	58.7	30.0	17.1	Average
Bath	Measured	Achievable	Required	Actual
Tap	Temp	Temp	Output	Output
LPM	DegC	DegC	KW	KW
14.6	31.7	41.5	30.0	20.0
14.1	34.6	42.6	30.0	22.2
14.3	33.2	42.1	30.0	21.1	Average
Bath	Measured	Achievable	Required	Actual
Tap	Temp	Temp	Output	Output
LPM	DegC	DegC	KW	KW
3.08	41.2	60	10.3	6.3
2.34	41.4	60	7.8	4.8
2.71	41.3	60	9.1	5.5	Average

j3oeff · Jan 16, 2022

John.g said:
This is the icing on the cake j3, (I was looking for 20kw or something like that) as it proves beyond all doubt that when one tap is throttled in, the boiler only produces ~ 60% of the required output even though very well within its rated output.

DHW
Boiler
Mains
Setpoint
Rated

Temp
Temp
Output

DegC
DegC
KW

12
60
30

Measured
Achievable
Required
Actual

Kitchen
Temp
Temp
Output
Output

LPM
DegC
DegC
KW
KW

5.6
47
60
18.6
13.6

5.6
43.5
60
18.8
12.4

5.7
42.9
60
19.0
12.3

5.8
42.3
60
19.4
12.3

5.7
43.9
60.0
19.0
12.6
Average
Downstairs

Bathroom
Measured
Achievable
Required
Actual

Tap
Temp
Temp
Output
Output

LPM
DegC
DegC
KW
KW

9.6
37.7
56.6
30.0
17.3

9.0
36.3
59.9
30.0
15.2

9.3
37.0
58.3
30.0
16.2
Average
Upstairs

Bathroom
Measured
Achievable
Required
Actual

Tap
Temp
Temp
Output
Output

LPM
DegC
DegC
KW
KW

10.1
35.0
54.7
30.0
16.2
11.1
34.9
50.7
30.0
17.8
10.6
35.0
52.7
30.0
17.0
Average
Ensuite
Sink
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
LPM
DegC
DegC
KW
KW
9.0
37.8
59.8
30.0
16.2
9.4
39.3
57.7
30.0
17.9
9.2
38.6
58.7
30.0
17.1
Average
Bath
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
LPM
DegC
DegC
KW
KW
14.6
31.7
41.5
30.0
20.0
14.1
34.6
42.6
30.0
22.2

14.3
33.2
42.1
30.0
21.1
Average
Bath
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
LPM
DegC
DegC
KW
KW
3.08
41.2
60
10.3
6.3

2.34
41.4
60
7.8
4.8

2.71
41.3
60
9.1
5.5
Average

Should be interesting to see what the engineer has to say tomorrow. I'll explain the situation and show him the info above. I'll let you know what has happened

j3oeff · Jan 17, 2022

So, according to the Baxi Engineer, I have a faulty Thermistor. He didn't have one with him so is coming back on Friday to fit a new one.

j3oeff · Jan 17, 2022

Forgot to add, he didn't seem keen on listening to the outputs, etc. Asked me where I got all that from and asked if they are heating engineers or not. I'm glad he checked the kitchen tap though as that probably offers the best heat currently and even he didn't move his hand once with the hot tap running.

John.g · Jan 17, 2022

I suppose a experienced service guy doesn't need a flow cup and thermometer to tell him that a kitchen tap should be almost scalding hot, fortunate in a way that had the reduced output only showed up in the shower, I wonder how would he have diagnosed the reduced bath output of 21kw, his hand would scarcely have informed him that the flow temp was only 33C but should have been 42C. I hope new combi boilers with your problems are few and far between.

j3oeff · Jan 17, 2022

I hope so too. Hopefully, this is just an unfortunate one-off and once resolved I will have boiler-free troubles. I certainly did not envisage spending £1900 on a new boiler and 2/3 weeks later have an issue. Peace of mind is the 10-year warranty I guess!

j3oeff · Jan 20, 2022

Genuinely think my old broken boiler worked better than this one haha. Turned heating on around 4.30pm via hive from work and just got home to this.

ShaunCorbs · Jan 20, 2022

Pressure is down need to fill the system

j3oeff · Jan 20, 2022

ShaunCorbs said:
Pressure is down need to fill the system

Yes I managed to find out what it was on Google. Is that normal though? Pressure to drop below 1bar from a new installation on Xmas Eve? Or could it be down to the 2 faulty radiator valves I have? Maybe letting small amounts of air out?

ShaunCorbs · Jan 20, 2022

Might be just all the air has settled and you haven’t seen the pressure is slightly low happens winthin a month of a new boiler / system as there’s a bit of air trapped etc

John.g · Jan 20, 2022

Tomorrow is D day, hopefully you will then be be luxuriating in a bath of HOT water with a bottle or two of champagne.

j3oeff · Jan 21, 2022

John.g said:
Tomorrow is D day, hopefully you will then be be luxuriating in a bath of HOT water with a bottle or two of champagne.

No champagne here my friend. We are expecting our first child so the wife can't drink and doesn't approve if I do without her haha.

Anyway, we have hot water

Few 1l approx fills runs and timings.

Bath sink
7.12 - 52.4c
6.98 - 54.7c

Bath tap
6.11 - 53.7c
7.67 - 48.4c

Ensuite
8.39 - 56.4c
9.10 - 53c

I certainly cannot hold my hand under any of the hot water taps for long now.

ShaunCorbs · Jan 21, 2022

Looks much better

What did he do ?

John.g · Jan 21, 2022

Can you measure the mains temp please.

j3oeff · Jan 21, 2022

ShaunCorbs said:
Looks much better

What did he do ?

Replaced a faulty thermistor

j3oeff · Jan 21, 2022

John.g said:
Can you measure the mains temp please.

Kitchen one?

John.g · Jan 21, 2022

Anywhere that's representative of the cold mains entering the boiler so cold kitchen tap should be OK after a few minutes run. You might also take two readings from the hot kitchen tap as that was very poor before.

John.g · Jan 21, 2022

Here are preliminary calculations, awaiting mains temperature but probably won't make a huge difference.

		DHW	Boiler
	Mains	Setpoint	Rated
	Temp	Temp	Output
	DegC	DegC	KW
	12	60	30
	Downstairs
	Bathroom	Measured	Achievable	Required	Actual
	Tap	Temp	Temp	Output	Output
Bath sink	LPM	DegC	DegC	KW	KW
7.12 - 52.4c	8.4	52.4	60.0	28.2	23.8
6.98 - 54.7c	8.6	54.7	60.0	28.8	25.6
	8.5	53.6	60.0	28.5	24.7	Average
	Ensuite
	Sink	Measured	Achievable	Required	Actual
	Tap	Temp	Temp	Output	Output
Ensuite	LPM	DegC	DegC	KW	KW
8.39 - 56.4c	7.2	56.4	60.0	23.9	22.2
9.10 - 53c	6.6	53.0	60.0	22.1	18.9
	6.9	54.7	60.0	23.0	20.5	Average
	Bath	Measured	Achievable	Required	Actual
	Tap	Temp	Temp	Output	Output
Bath tap	LPM	DegC	DegC	KW	KW
6.11 - 53.7c	9.82	53.7	55.8	30.0	28.6
7.67 - 48.4c	7.82	48.4	67.0	30.0	19.9
	8.82	51.05	60.7	30.0	24.2	Average

j3oeff · Jan 21, 2022

Cold tap in kitchen is 7c and filled in 10.04

Hot tap kitchen

10.90 - 57.5c
10.77 - 57c

I've just had a shower and the thermostat tap was set to 50c but it was no way that. I think I may have a broken valve or something. How would I be able to find out?

j3oeff · Jan 21, 2022

John.g said:
Here are preliminary calculations, awaiting mains temperature but probably won't make a huge difference.

DHW
Boiler
Mains
Setpoint
Rated

Temp
Temp
Output

DegC
DegC
KW

12
60
30

Downstairs

Bathroom
Measured
Achievable
Required
Actual

Tap
Temp
Temp
Output
Output

Bath sink
LPM
DegC
DegC
KW
KW

7.12 - 52.4c
8.4
52.4
60.0
28.2
23.8

6.98 - 54.7c
8.6
54.7
60.0
28.8
25.6

8.5
53.6
60.0
28.5
24.7
Average
Ensuite
Sink
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
Ensuite
LPM
DegC
DegC
KW
KW
8.39 - 56.4c
7.2
56.4
60.0
23.9
22.2
9.10 - 53c
6.6
53.0
60.0
22.1
18.9
6.9
54.7
60.0
23.0
20.5
Average
Bath
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
Bath tap
LPM
DegC
DegC
KW
KW
6.11 - 53.7c
9.82
53.7
55.8
30.0
28.6

7.67 - 48.4c
7.82
48.4
67.0
30.0
19.9

8.82
51.05
60.7
30.0
24.2
Average

I've noticed the jug fills have taken longer and some are a little less LPM. Any reason for that? One thing i use to get with the old boiler when turning the hot taps on upstairs was a clunk type noise which sounded like something was kicking in and hot water started flowing.

That went away when new boiler was installed but has for some reason now returned. Odd

ShaunCorbs · Jan 21, 2022

He hasn’t slightly closed the 2nd in from the right going from right to left has he ?

John.g · Jan 21, 2022

Final calculations, cold mains, 7.0C.

Definitely appears a (good) bit shy of full output, say 5/6kw, which may need verifying with gas meter monitoring, I wouldn't be too happy with the above to be honest as you might only effectively have a 24/25 kw shower.

You might also do the bath tap at its full output of ~ 14LPM.

Re Shower: IF the boiler output was/is 30kw then you will get 10.0 LPM at 50C. (from cold at 7C)
If the boiler output is indeed say 25kw then you will get 8.3LPM
or at a showering temp of 40C, the numbers are 13.03LPM & 10.9LPM.
Suggest you measure the flow and temperature from the shower as well.

		DHW	Boiler
	Mains	Setpoint	Rated
	Temp	Temp	Output
	DegC	DegC	KW
	7	60	30
	Downstairs
	Bathroom	Measured	Achievable	Required	Actual
	Tap	Temp	Temp	Output	Output
Bath sink	LPM	DegC	DegC	KW	KW
7.12 - 52.4c	8.4	52.4	58.0	30.0	23.8
6.98 - 54.7c	8.6	54.7	57.0	30.0	25.6
	8.5	53.6	57.5	30.0	24.7	Average
	Ensuite
	Sink	Measured	Achievable	Required	Actual
	Tap	Temp	Temp	Output	Output
Ensuite	LPM	DegC	DegC	KW	KW
8.39 - 56.4c	7.2	56.4	60.0	26.4	22.2
9.10 - 53c	6.6	53.0	60.0	24.4	18.9
	6.9	54.7	60.0	25.4	20.5	Average
		Measured	Achievable	Required	Actual
	Kitchen	Temp	Temp	Output	Output
kitchen	LPM	DegC	DegC	KW	KW
10.90 - 57.5c	5.5	57.3	60	18.4	17.4
10.77 - 57c	5.6	57	60	18.7	17.5
	5.5	57.2	60.0	18.5	17.4	Average
	Bath	Measured	Achievable	Required	Actual
	Tap	Temp	Temp	Output	Output
Bath tap	LPM	DegC	DegC	KW	KW
6.11 - 53.7c	9.82	53.7	50.8	30.0	28.6
7.67 - 48.4c	7.82	48.4	62.0	30.0	19.9
	8.82	51.05	55.7	30.0	24.2	Average

John.g · Jan 21, 2022

I presume thermostatic showers have a flow control "knob" as well as the temperature setting, because if not then if the thermostat is closing off the cold water completely, as it should, the temp can still be too low depending on the hot flowrate through the shower and the boiler output?.
So maybe nothing wrong with the thermostatic control?.

j3oeff · Jan 21, 2022

John.g said:
Final calculations, cold mains, 7.0C.

Definitely appears a (good) bit shy of full output, say 5/6kw, which may need verifying with gas meter monitoring, I wouldn't be too happy with the above to be honest as you might only effectively have a 24/25 kw shower.

You might also do the bath tap at its full output of ~ 14LPM.

Re Shower: IF the boiler output was/is 30kw then you will get 10.0 LPM at 50C. (from cold at 7C)
If the boiler output is indeed say 25kw then you will get 8.3LPM
or at a showering temp of 40C, the numbers are 13.03LPM & 10.9LPM.
Suggest you measure the flow and temperature from the shower as well.

DHW
Boiler
Mains
Setpoint
Rated

Temp
Temp
Output

DegC
DegC
KW

7
60
30

Downstairs

Bathroom
Measured
Achievable
Required
Actual

Tap
Temp
Temp
Output
Output

Bath sink
LPM
DegC
DegC
KW
KW

7.12 - 52.4c
8.4
52.4
58.0
30.0
23.8

6.98 - 54.7c
8.6
54.7
57.0
30.0
25.6

8.5
53.6
57.5
30.0
24.7
Average
Ensuite
Sink
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
Ensuite
LPM
DegC
DegC
KW
KW
8.39 - 56.4c
7.2
56.4
60.0
26.4
22.2
9.10 - 53c
6.6
53.0
60.0
24.4
18.9
6.9
54.7
60.0
25.4
20.5
Average

Measured
Achievable
Required
Actual

Kitchen
Temp
Temp
Output
Output

kitchen
LPM
DegC
DegC
KW
KW

10.90 - 57.5c
5.5
57.3
60
18.4
17.4

10.77 - 57c
5.6
57
60
18.7
17.5

5.5
57.2
60.0
18.5
17.4
Average
Bath
Measured
Achievable
Required
Actual
Tap
Temp
Temp
Output
Output
Bath tap
LPM
DegC
DegC
KW
KW
6.11 - 53.7c
9.82
53.7
50.8
30.0
28.6

7.67 - 48.4c
7.82
48.4
62.0
30.0
19.9

8.82
51.05
55.7
30.0
24.2
Average

Shower set at 50 on tap
6.68 - 35c

Shower set at 45 on tap
6.74 - 35.1c

Shower set at 38 on tap
6.40 - 35.1c

Are you saying I could still achieve hotter water of the boiler was outputting 5/6kwh more. How would I measure the gas readings to investigate further if so?

j3oeff · Jan 21, 2022

ShaunCorbs said:
He hasn’t slightly closed the 2nd in from the right going from right to left has he ?

The pressure switch?

John.g · Jan 21, 2022

j3oeff said:
Shower set at 50 on tap
6.68 - 35c

Shower set at 45 on tap
6.74 - 35.1c

Shower set at 38 on tap
6.40 - 35.1c

Are you saying I could still achieve hotter water of the boiler was outputting 5/6kwh more. How would I measure the gas readings to investigate further if so?

As before, open the hot bath tap fully, measure its flowrate&temp, then leave it running and monitor the gas meter readings for exactly 2 minutes again.

j3oeff · Jan 21, 2022

John.g said:
As before, open the hot bath tap fully, measure its flowrate&temp, then leave it running and monitor the gas meter readings for exactly 2 minutes again.

Ok. will do tomorrow and come back with findings.

ShaunCorbs · Jan 21, 2022

j3oeff said:
The pressure switch?

The iso under neath the boiler eg black lever

2nd one in from the right side 15mm

John.g · Jan 21, 2022

Shower calcs attached,

			DHW	Boiler
		Mains	Setpoint	Rated
		Temp	Temp	Output
		DegC	DegC	KW
		7	60	30
		Downstairs
		Bathroom	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Bath sink	LPM	DegC	DegC	KW	KW
	7.12 - 52.4c	8.4	52.4	58.0	30.0	23.8
	6.98 - 54.7c	8.6	54.7	57.0	30.0	25.6
		8.5	53.6	57.5	30.0	24.7	Average
		Ensuite
		Sink	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Ensuite	LPM	DegC	DegC	KW	KW
	8.39 - 56.4c	7.2	56.4	60.0	26.4	22.2
	9.10 - 53c	6.6	53.0	60.0	24.4	18.9
		6.9	54.7	60.0	25.4	20.5	Average
			Measured	Achievable	Required	Actual
		Kitchen	Temp	Temp	Output	Output
	kitchen	LPM	DegC	DegC	KW	KW
	10.90 - 57.5c	5.5	57.3	60	18.4	17.4
	10.77 - 57c	5.6	57	60	18.7	17.5
		5.5	57.2	60.0	18.5	17.4	Average
		Bath	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Bath tap	LPM	DegC	DegC	KW	KW
	6.11 - 53.7c	9.82	53.7	50.8	30.0	28.6
	7.67 - 48.4c	7.82	48.4	62.0	30.0	19.9
		8.82	51.05	55.7	30.0	24.2	Average
			Measured	Required	Required	Actual
		Shower	Temp	Temp	Output	Output
		LPM	DegC	DegC	KW	KW
Shower. SP 50C	6.68 - 35c	8.98	35.0	50.0	26.9	14.4
Shower. SP 45C	6.74 - 35.1c	8.90	35.1	45.0	23.6	14.3
Showr. SP 38C	6.4 - 35.1c	9.38	35.1	38.0	20.3	15.1
		9.09	35.07	44.33	23.61	14.62	Average

John.g · Jan 22, 2022

Corrected calculations (done at 12C) should have been 7C.

Looking a lot better now, so checks tomorrow will verify.

Shower discrepancies probably due to mixing problems, thermostat etc, to be determined.

			DHW	Boiler
		Mains	Setpoint	Rated
		Temp	Temp	Output
		DegC	DegC	KW
		7	60	30
		Downstairs
		Bathroom	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Bath sink	LPM	DegC	DegC	KW	KW
	7.12 - 52.4c	8.4	52.4	58.0	30.0	26.7
	6.98 - 54.7c	8.6	54.7	57.0	30.0	28.6
		8.5	53.6	57.5	30.0	27.6	Average
		Ensuite
		Sink	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Ensuite	LPM	DegC	DegC	KW	KW
	8.39 - 56.4c	7.2	56.4	60.0	26.4	24.6
	9.10 - 53c	6.6	53.0	60.0	24.4	21.2
		6.9	54.7	60.0	25.4	22.9	Average
			Measured	Achievable	Required	Actual
		Kitchen	Temp	Temp	Output	Output
	kitchen	LPM	DegC	DegC	KW	KW
	10.90 - 57.5c	5.5	57.3	60.0	20.4	19.3
	10.77 - 57c	5.6	57	60	20.6	19.4
		5.5	57.2	60.0	20.5	19.4	Average
		Bath	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Bath tap	LPM	DegC	DegC	KW	KW
	6.11 - 53.7c	9.82	53.7	50.8	30.0	32.0
	7.67 - 48.4c	7.82	48.4	62.0	30.0	22.6
		8.82	51.05	55.7	30.0	27.3	Average
			Measured	Achievable	Required	Actual
		Shower	Temp	Temp	Output	Output
		LPM	DegC	DegC	KW	KW
Shower. SP 50C	6.68 - 35c	8.98	35.0	54.9	30.0	17.5
Shower. SP 45C	6.74 - 35.1c	8.90	35.1	55.3	30.0	17.5
Showr. SP 38C	6.4 - 35.1c	9.38	35.1	52.9	30.0	18.4
		9.09	35.07	54.35	30.00	17.79	Average

j3oeff · Jan 22, 2022

Bath tap run today

6.45 - 48c
6.36 - 48.5c
6.11 - 48.6c

Full 2 minute tap run

Gas reading start - 456.228
Gas reading finish - 456.372

j3oeff · Jan 22, 2022

ShaunCorbs said:
The iso under neath the boiler eg black lever

2nd one in from the right side 15mm

Nothing looks closer to me?

John.g · Jan 22, 2022

4 min gas readings, 456.372-456.228 = 0.144 = 2.16M3/hr = 2.16*11.3. 24.41Kwh
Assume boiler efficiency at 90% = boiler output of 24.41*0.9 = 21.97kwh (22kw output boiler)
but your retested bath tap calculations show a calculated requirement of 27.5Kw so something not adding up here, you were able to get flow rates of ~ 14LPM from the bath tap a few days ago, so why not now?.

Bath tap

4.12 - 31.7c

4.27 - 34.6c

60/4.12 = 14.56LPM. 60/14.05LPM.
We have to be absolutely sure that the HW demand is well > than the boiler output and then do the gas meter check again
SO, either get a set of readings from the bath tap full open but if you cannot get more than the 8.9LPM at todays test, just open another hot tap, take the readings from both taps, let both taps open and do your 2 minute gas meter test again and that will finally prove the boiler output.
Also for accuracy, have a look at one of your gas bills and note the gas usage in M3, the gas usage is also converted to Kwh so divide the Kwh by the M3 used and that will give the Kwh/M3. I am using 11.3kwh/M3 from some user on another thread here.

			DHW	Boiler
		Mains	Setpoint	Rated
		Temp	Temp	Output
		DegC	DegC	KW
		7	60	30
		Downstairs
		Bathroom	Measured	Achievable	Required	Calcul
		Tap	Temp	Temp	Output	Output
	Bath sink	LPM	DegC	DegC	KW	KW
	7.12 - 52.4c	8.4	52.4	58.0	30.0	26.7
	6.98 - 54.7c	8.6	54.7	57.0	30.0	28.6
		8.5	53.6	57.5	30.0	27.6	Average
		Ensuite
		Sink	Measured	Achievable	Required	Calcul
		Tap	Temp	Temp	Output	Output
	Ensuite	LPM	DegC	DegC	KW	KW
	8.39 - 56.4c	7.2	56.4	60.0	26.4	24.6
	9.10 - 53c	6.6	53.0	60.0	24.4	21.2
		6.9	54.7	60.0	25.4	22.9	Average
			Measured	Achievable	Required	Calcul
		Kitchen	Temp	Temp	Output	Output
	kitchen	LPM	DegC	DegC	KW	KW
	10.90 - 57.5c	5.5	57.3	60.0	20.4	19.3
	10.77 - 57c	5.6	57	60	20.6	19.4
		5.5	57.2	60.0	20.5	19.4	Average
		Bath	Measured	Achievable	Required	Calcul
		Tap	Temp	Temp	Output	Output
	Bath tap	LPM	DegC	DegC	KW	KW
	6.11 - 53.7c	9.82	53.7	50.8	30.0	32.0
	7.67 - 48.4c	7.82	48.4	62.0	30.0	22.6
		8.82	51.05	55.7	30.0	27.3	Average
		Bath	Measured	Achievable	Required	Calcul
	Retest	Tap	Temp	Temp	Output	Output
	bath tap	LPM	DegC	DegC	KW	KW
	6.45 48c	9.30	48	53.2	30.0	26.6
	6.36 48.5	9.43	48.5	52.6	30.0	27.3
	6.11 48.6c	9.82	48.5	50.8	30.0	28.4
		9.52	48.3	52.2	30.0	27.5	Average
			Measured	Achievable	Required	Calcul
		Shower	Temp	Temp	Output	Output
Shower. SP 50C	6.68 - 35c	LPM	DegC	DegC	KW	KW
Shower. SP 45C	6.74 - 35.1c	8.98	35.0	54.9	30.0	17.5
Showr. SP 38C	6.4 - 35.1c	8.90	35.1	55.3	30.0	17.5
		9.38	35.1	52.9	30.0	18.4
		9.09	35.07	54.35	30.00	17.79	Average

j3oeff · Jan 22, 2022

With regards to previous flows,I have no idea why it is now slightly slower. I don't know if the engineer changed something or adjusted something. Like I mentioned above, I now have the noise inuse to have with the old boiler when switching hot water taps on which disappeared initially upon new install.

I've ran both hot water taps in the bathroom and the readings are below.

Gas start readings 456.977m3

Gas reading finish - 457.064m3

What am I looking for on gas bill usage btw?

John.g · Jan 22, 2022

Something like this, you might see about 5 lines down from the top left corner " consumption (110.9) M3 and energy used directly below it, (1257.3) kwh.

Presume below is a 2 Minute reading??
2 min gas readings, 457.064-456.977 = 0.087= 2.61M3/hr = 2.61*11.3 = 29.49Kwh. Boiler efficiency of 90% = 29.49*0.9 = 26.5kwh, short fall of 3.5kw so I suppose nearly there??.

The bath flow rate is IMO drastically reduced for whatever reason, if you were getting 14.5LPM at say a mains pressure of 4 bar, the pressure (mains or otherwise) is now only around 1.54 bar to give a flow rate of 9LPM.

j3oeff · Jan 22, 2022

Sorry yes,those are 2 minute tap runs.

I honestly don't know why the flow rate has dropped off, its only since the engineer visit.

Attached screenshots

John.g · Jan 22, 2022

Your gas usage was 152.1M3 which was converted to 1719.1Kwh = 11.302kwh/M3 which was the number I used in the calculations. (11.3)
If the engineer you are referring to was the Gas Engineer then he must have throttled the mains flow to the boiler, I don't think that's a good practice, the end user, IMO can do his own throttling at his own taps/shower etc, it may also play havoc with your shower mixer if the hot water pressure is now way lower than the cold pressure.
Can you do a quick check on your bath cold water flow, just the flow with the tap opened fully for say 2 minutes, this might tell you something.

j3oeff · Jan 22, 2022

John.g said:
Your gas usage was 152.1M3 which was converted to 1719.1Kwh = 11.302kwh/M3 which was the number I used in the calculations. (11.3)
If the engineer you are referring to was the Gas Engineer then he must have throttled the mains flow to the boiler, I don't think that's a good practice, the end user, IMO can do his own throttling at his own taps/shower etc, it may also play havoc with your shower mixer if the hot water pressure is now way lower than the cold pressure.
Can you do a quick check on your bath cold water flow, just the flow with the tap opened fully for say 2 minutes, this might tell you something.

Will do. I'm not measuring anything am I or looking for something?

John.g · Jan 22, 2022

If the hot & cold taps are the same size/type then one might expect the flowrates to be similar when fully opened so if you find the cold tap flowing 12 to 14 LPM (the hot is presently ~ 9LPM) then obvious throttling going on somewhere.
Some combi boilers have restrictors installed to limit the flowrate to give a dT of 35C through the boiler, a 30kw boiler will give a flowrate of 30*860/60/35,12.3LPM. with a temperature rise (dT) of 35C.

ShaunCorbs · Jan 22, 2022

All looks good to me maybe there was a fault flow regulator inside the boiler as well causing too much flow through the plate compounded by the fault hw thermistor

Glad your happy and have a working boiler to correct spec

j3oeff · Jan 22, 2022

John.g said:
If the hot & cold taps are the same size/type then one might expect the flowrates to be similar when fully opened so if you find the cold tap flowing 12 to 14 LPM (the hot is presently ~ 9LPM) then obvious throttling going on somewhere.
Some combi boilers have restrictors installed to limit the flowrate to give a dT of 35C through the boiler, a 30kw boiler will give a flowrate of 30*860/60/35,12.3LPM. with a temperature rise (dT) of 35C.

Cold water from bath tip is filling a 1 litre jug in around 2.10 seconds and it was consistent on about 6 fills.

j3oeff · Jan 22, 2022

ShaunCorbs said:
All looks good to me maybe there was a fault flow regulator inside the boiler as well causing too much flow through the plate compounded by the fault hw thermistor

Glad your happy and have a working boiler to correct spec

I am happy now yes. Just glad to finally have hot water and be able to take baths and also keeps the wife happy.

I will however have to investigate the shower further as there is an issue with that and the temperature not being correct .

John.g · Jan 22, 2022

That's some flow through the cold tap at 28.5LPM, the hot and cold pressures to any mixer should be more or less the same, I think within a 0.5 to 1bar of each other to get satisfactory mixing so possibly some problem with a PRV on the cold supply to the shower or whereever. . Probably have to get a plumber to investigate this.

ShaunCorbs · Jan 22, 2022

j3oeff said:
I am happy now yes. Just glad to finally have hot water and be able to take baths and also keeps the wife happy.

I will however have to investigate the shower further as there is an issue with that and the temperature not being correct .

Have you tried cleaning the filters/ strainer in the shower ?

j3oeff · Jan 22, 2022

ShaunCorbs said:
Have you tried cleaning the filters/ strainer in the shower ?

It's a new shower head so shouldn't be the issue. The issue started with the old boiler where it was boiling hot even on 38c. Had to turn it right down to 25c and then it was ice cold so that's why I was thinking an issue with the tap itself?

j3oeff · Jan 22, 2022

John.g said:
That's some flow through the cold tap at 28.5LPM, the hot and cold pressures to any mixer should be more or less the same, I think within a 0.5 to 1bar of each other to get satisfactory mixing so possibly some problem with a PRV on the cold supply to the shower or whereever. . Probably have to get a plumber to investigate this.

It is abit odd. It was previously working fine months ago but as the old boiler deteriorated the shower temps started playing up and have continued with the new boiler.

ShaunCorbs · Jan 22, 2022

j3oeff said:
It's a new shower head so shouldn't be the issue. The issue started with the old boiler where it was boiling hot even on 38c. Had to turn it right down to 25c and then it was ice cold so that's why I was thinking an issue with the tap itself?

Yes sounds like the shower cartridge has gone

John.g · Jan 22, 2022

Shaun was referring to filters which may be installed where the mixer bar connects to the pipework but would require hot and cold water isolation somewhere.

Not sure, what this will prove, if anything, but maybe turn the shower temperature setting to max then reduce the Boiler DHW temp setting to 40Cish and monitor flow/temp.

j3oeff · Jan 23, 2022

John.g said:
Shaun was referring to filters which may be installed where the mixer bar connects to the pipework but would require hot and cold water isolation somewhere.

Not sure, what this will prove, if anything, but maybe turn the shower temperature setting to max then reduce the Boiler DHW temp setting to 40Cish and monitor flow/temp.

Will give that a go.

I assume I can isolate the water upstairs and then take the mixer tap apart to check filters etc and give it a clean/descale or replace.

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