New Boiler to replace a old Worcester 35CDi II

[John.g]

So I've just done some jug filling tests with times and temps. Not one room upstairs gets above 42c

Kitchen tap (closest to boiler)
12.09 secs @ 42.4c
18.10 secs @ 54.4c

Bathroom ensuite
12.82 secs @ 39.4c
20.31 secs @ 43.1c

Main bathroom sink
12.51 secs @ 35.1c
21.83 secs @ 41.1c

Bath
4.13 secs @ 31.8c
11.43 secs @ 39.1c
13.07 secs @ 39.9c
13.47 secs @ 41.2c
17.68 secs @ 41.7c
18.94 secs @ 41.6c
21.62 secs @ 41.2c

Flow Rates & Boiler Outputs based on data above: assuming cold mains at 9C

12.09 secs @ 42.4c 4.96LPM, 11.6kw
18.10 secs @ 54.4c 3.31LPM, 10.48kw

Bathroom ensuite
12.82 secs @ 39.4c 4.68LPM, 9.93kw
20.31 secs @ 43.1c

Main bathroom sink
12.51 secs @ 35.1c 4.79LPM, 8.72kw
21.83 secs @ 41.1c 2.74LPM, 6.14kw

Bath
4.13 secs @ 31.8c 14.52LPM, 23kw
11.43 secs @ 39.1c 5.24LPM, 11kw
13.07 secs @ 39.9c 4.59LPM, 9.9kw
13.47 secs @ 41.2c 4.45LPM, 10kw
17.68 secs @ 41.7c 3.39LPM,7.73kw
18.94 secs @ 41.6c 4.68LPM, 9.93kw
21.62 secs @ 41.2c 3.17LPM. 7.12kw

Reply
Looks like the flows are too low or there is a flow switch problem as the only output that looks like a constantly firing boiler is 4.13 secs @ 31.8c 14.52LPM, 23kw
I think the minimum output of this boiler is 8kw?? so requires a minimum flowrate of 2.25LPM to avoid temperature exceeding 60C, flow switch possibly set to 3/3.5LPM???perhaps faulty??. There is certainly a boiler problem somewhere IMO.

 

[j3oeff]

Flow Rates & Boiler Outputs based on data above: assuming cold mains at 9C

12.09 secs @ 42.4c 4.96LPM, 11.6kw
18.10 secs @ 54.4c 3.31LPM, 10.48kw

Bathroom ensuite
12.82 secs @ 39.4c 4.68LPM, 9.93kw
20.31 secs @ 43.1c

Main bathroom sink
12.51 secs @ 35.1c 4.79LPM, 8.72kw
21.83 secs @ 41.1c 2.74LPM, 6.14kw

Bath
4.13 secs @ 31.8c 14.52LPM, 23kw
11.43 secs @ 39.1c 5.24LPM, 11kw
13.07 secs @ 39.9c 4.59LPM, 9.9kw
13.47 secs @ 41.2c 4.45LPM, 10kw
17.68 secs @ 41.7c 3.39LPM,7.73kw
18.94 secs @ 41.6c 4.68LPM, 9.93kw
21.62 secs @ 41.2c 3.17LPM. 7.12kw

Reply
Looks like the flows are too low or there is a flow switch problem as the only output that looks like a constantly firing boiler is 4.13 secs @ 31.8c 14.52LPM, 23kw
I think the minimum output of this boiler is 8kw?? so requires a minimum flowrate of 2.25LPM to avoid temperature exceeding 60C, flow switch possibly set to 3/3.5LPM???perhaps faulty??. There is certainly a boiler problem somewhere IMO.

Flow Rates & Boiler Outputs based on data above: assuming cold mains at 9C

12.09 secs @ 42.4c 4.96LPM, 11.6kw
18.10 secs @ 54.4c 3.31LPM, 10.48kw

Bathroom ensuite
12.82 secs @ 39.4c 4.68LPM, 9.93kw
20.31 secs @ 43.1c

Main bathroom sink
12.51 secs @ 35.1c 4.79LPM, 8.72kw
21.83 secs @ 41.1c 2.74LPM, 6.14kw

Bath
4.13 secs @ 31.8c 14.52LPM, 23kw
11.43 secs @ 39.1c 5.24LPM, 11kw
13.07 secs @ 39.9c 4.59LPM, 9.9kw
13.47 secs @ 41.2c 4.45LPM, 10kw
17.68 secs @ 41.7c 3.39LPM,7.73kw
18.94 secs @ 41.6c 4.68LPM, 9.93kw
21.62 secs @ 41.2c 3.17LPM. 7.12kw

Reply
Looks like the flows are too low or there is a flow switch problem as the only output that looks like a constantly firing boiler is 4.13 secs @ 31.8c 14.52LPM, 23kw
I think the minimum output of this boiler is 8kw?? so requires a minimum flowrate of 2.25LPM to avoid temperature exceeding 60C, flow switch possibly set to 3/3.5LPM???perhaps faulty??. There is certainly a boiler problem somewhere IMO.

Central Heating Max. Output	21.2 kW
Mounting	Wall Mounted
Flow Rate	12.2 l/min

If I was to fill a bath at 14.52lpm does that mean the bath would be 31.8c ?

I think I'll have to get the installer back in the new year for further investigation.

 

[ShaunCorbs]

Can you take a picture of the boiler please ?

 

[j3oeff]

Can you take a picture of the boiler please ?

 

[ShaunCorbs]

There should be a slide out tab on the left or right underside of the front if you look under you will see it

 

[John.g]

Central Heating Max. Output	21.2 kW
Mounting	Wall Mounted
Flow Rate	12.2 l/m

If I was to fill a bath at 14.52lpm does that mean the bath would be 31.8c ?

I think I'll have to get the installer back in the new year for further investigation.

That's right but if the boiler was at its rated output of 30kw then the HW temperature would be almost 39C (38.6C). If you required a bath filling temp of say 45C then you would have to reduce the flowrate to just under12LPM (11.94) again assuming boiler at its rated 30kw output.

The 21.2kw output above is the output when on CH duty only.

If you like sometime you might take one more test of that bath flowrate and temperature and also the cold mains temperature to really tie down the actual boiler output very accurately.

 

[ShaunCorbs]

That's right but if the boiler was at its rated output of 30kw then the HW temperature would be almost 39C (38.6C). If you required a bath filling temp of say 45C then you would have to reduce the flowrate to just under12LPM (11.94) again assuming boiler at its rated 30kw output.

The 21.2kw output above is the output when on CH duty only.

If you like sometime you might take one more test of that bath flowrate and temperature and also the cold mains temperature to really tie down the actual boiler output very accurately.

Or a 25kw which I think might be the issue maybe

 

[j3oeff]

There should be a slide out tab on the left or right underside of the front if you look under you will see it

 

[ShaunCorbs]

Best call baxi out as your having low kw rates out of your bath taps

 

[j3oeff]

That's right but if the boiler was at its rated output of 30kw then the HW temperature would be almost 39C (38.6C). If you required a bath filling temp of say 45C then you would have to reduce the flowrate to just under12LPM (11.94) again assuming boiler at its rated 30kw output.

The 21.2kw output above is the output when on CH duty only.

If you like sometime you might take one more test of that bath flowrate and temperature and also the cold mains temperature to really tie down the actual boiler output very accurately.

Various tape flows

Cold

2.11 secs @ 7.5c
2.17 secs @ 7.5c

Hot
3.74 secs @ 31.2c
3.86 secs @ 33.7c
6.30 secs @ 36c
10.16 secs @ 39.8c
16.26 secs @ 41c

 

[j3oeff]

Best call baxi out as your having low kw rates out of your bath taps

Baxi rather than installer?

Best call baxi out as your having low kw rates out of your bath taps

 

[ShaunCorbs]

I would say so as I’m guessing your bath taps don’t have flow restrictiors in hence the correct flow rate and your only pulling on johns calculations 23kw

You can prove this by taking a gas meter reading then run the tap for 2 mins and take another reading and come back to us (aslong as it’s a metric meter eg not in ft/h

 

[John.g]

Measured Mains temp 7.5C

3.74 secs @ 31.2c 16.04LPM 26.52kw
3.86 secs @ 33.7c 15.54LPM 28.4kw
6.30 secs @ 36c 9.52LPM 18.92kw
10.16 secs @ 39.8c 5.91LPM 13.31kw
16.26 secs @ 41c 3.69LPM 8.62kw

Edit: Also corrected kw from post 31, mains are 7.5C, assumed originally at 9C.
4.13 secs @ 31.8c 14.52LPM, 23kw corrected to 7.5C mains = 24.62kw

 

[j3oeff]

I would say so as I’m guessing your bath taps don’t have flow restrictiors in hence the correct flow rate and your only pulling on johns calculations 23kw

You can prove this by taking a gas meter reading then run the tap for 2 mins and take another reading and come back to us (aslong as it’s a metric meter eg not in ft/h

Before and after

 

[ShaunCorbs]

Sorry they don’t update fast enough needs to be the gas meter