Can someone explain how my boiler works!?

[MattC76]

Hi All,
I've been hunting around/reading manuals etc for ages but can't seem to get a definite answer and hope you guys might be able to help!

We've just moved into an old 5-bed victorian house and I'm not convinced I fully understand how the boiler works. The system consists of:

1. Worcester Greenstar 30cdi conventional boiler with Honeywell St9100A control panel
2. Hot water Cylinder with cylinder thermostat (currently set at 60degC)
3. A room thermostat in the hall (honeywell CM907) hardwired to the mains elec.
4. TRV's on all rads apart from in the hall where the thermostat is.

My questions are:

1. Will the boiler respond to the cylinder thermostat if the boiler is OFF on the ST9100A? Or is the cylinder thermostat independent of the ST9100A so that the cylinder temp is always 60C?
2. I currently have the temp controls on the boiler (i.e. the dial thingy!) set to max - I have heard this is most efficient - is that true?
3. Is it best to have the boiler set to CONTINUOUS on the ST9100A and use the programmable room thermostat to vary the temp at different times of day/night? Or should I program the boiler to come on in the morning and evening - which is most efficient?
4. We are currently using 3-4 imperial units of gas/day which is getting quite pricey to say the least (I have worked out roughly on our tariff to be about £3-£4 per day on gas alone! - is this about right for a biggish old house?

Thanks in advance and sorry to be a muppet!

Cheers,
Matt

 

[tamz]

1. No. You need to time when you want your water on the 9100. You set the HW times on the programmer and the cylinder stat closes the motorised valve (or turns off the boiler if no other demand) when the set temperature is reached.
2. Not usually with a condensing boiler. Setting it lower means the boiler condenses more and is cheaper to run. It needs to be set higher than the cylinder stat or the water will never reach the set temperature.
3. If you set the 9100 to continuous then you ae only setting your hot water to continuous. I doesn't control your heating.
The CM907 is a programmable rooms stat. It controls the times your heating turns on ond off and the maximum and minimum temperatures of your house. It functions independent of the 9100 timer.
Set the times you want your hot water to come on and off using the 9100 and set the heating times on the CM907. When you set for it is up to you but unless your house is very well insulated, it is probably better morning and night.
4. £3-4 a day is a lot even for a big old house. Set your timers correctly and if you have thermostatic valves on your radiators set them too.

 

[CES]

In addition to Tamz advice, make sure your TRVs are adjusted to your room temperature preferences and close all your doors in between the rooms otherwise they wont work correctly.

 

[stevetheplumber]

average bill for a three bed house is now reckoned to be between £1000 and £1200
£4 a day is £1460 so if its a big place would seem about right frightening realyi used to get a pounds worth of 10ps for the weeeks gas when we were on slot meter and we would get some back when it was emptied

 

[MattC76]

Thanks for the replies!

3. If you set the 9100 to continuous then you ae only setting your hot water to continuous. I doesn't control your heating.
The CM907 is a programmable rooms stat. It controls the times your heating turns on ond off and the maximum and minimum temperatures of your house. It functions independent of the 9100 timer.

When I program the 9100 to OFF, then the boiler seems to ignore all inputs from the CM907 room stat in the hall until the 9100 goes ON and then the rads come on. So should the 9100 and the CM907 work independently from each other because at the moment they don't!? It seems like the 9100 is the MASTER on/off switch!?

Thanks again.
Matt

 

[dontknowitall]

They should work independently. Sounds like the system hasn't been wired correctly.

 

[tamz]

If it is working as you say it has been wired wrong. It should be a simple job to fix it out.

How it should work in a set up like this is
The 9100, being a single channel programmer (time clock), only controls one part of the system, in this case only the HW side.
The CM907 is a stand alone programmable room stat, capable of operating the heating side on its own.

It should only be a matter of swapping a wire to make them independent.

 

[MattC76]

They should work independently. Sounds like the system hasn't been wired correctly.

Hmmm - I'll do a proper test although I am certain that they do not work independently. For example today I had set the 9100 to come on at 1630hrs. I arrived home early and the CM907 (which was set to 19C) read an actual temp of 17.5C, the flame "icon" (on the CM907) was displayed but the heating DID NOT come on until 1630hrs.

So are you saying that the 9100 controls only the hot water??

Matt

 

[MattC76]

Sorry cross posted I think!

We recently had the room above the boiler redecorated and a new plug socket fitted. The sparky somehow managed to drill through the wire for the room stat (CM907) such that the wire from the 907 was always live and the boiler always on despite being "off" on the controller!? Anyway it was the excellent Worcester engineer who worked out the problem (fortunately still under warranty) the sparkys came back sheepishly and "put it right" and did a few other little jobs for us by why of compensation. I'm just wondering whether it was installed incorrectly originally (2 yrs ago before we moved in) or whether the sparkys wired it back together incorrectly?
Matt

 

[dontknowitall]

9100 controls only the hot water.
CM907 controls only the heating.

If the flame icon was displayed it means the CM907 was calling for heat. If the boiler wasn't firing then the system's not wired correctly. The flame icon won't show unless the programmer is calling for heat (so if you have heating on in morning and evening but not during the day then the flame icon won't show during the day irrespective of the room temperature - unless it's low enough for the frost ....)

 

[tamz]

Does the 907 still control the heating ie turn it off when the temperature is reached?

 

[MattC76]

Does the 907 still control the heating ie turn it off when the temperature is reached?

Yes - the 907 seems to turn the heating on and off according to the actual temp and the target temp BUT will only work if the 9100 is ON i.e. in continuous mode or programmed to be ON at that particular time. When the 9100 is OFF the 907 has no control over the heating.

 

[tamz]

Either
As your CH motorised valve is faulty or it needs a wire swapping.

 

[MattC76]

Either
As your CH motorised valve is faulty or it needs a wire swapping.

Is that something the Worcester engineer would do under warranty?

 

[tamz]

Is that something the Worcester engineer would do under warranty?

No. It is a control. You will need a heating guy or an electrician.

 

[MattC76]

OK so its my day off so I've had a chance to have a fiddle (with the boiler!) and I really have no idea whats happening.

Basically yesterday I had set the 9100 to OFF at 0900hrs and the CM907 to target 16C at the same time expecting everything to switch off at 0900hrs. When I came home that evening my wife said the heating had been on all day and the house had got very hot! The 9100 had been set to come ON at 1630 hrs (which it did) and this caused everything to switch off - it seemed that the CM907 had regained control and was targeting 19C (the evening temperature that I had set), and indeed the radiators switched off until the target was reached and then came on (as they should).

Then today again everything failed to go off at 0900hrs and the boiler was still running - we had all had hot showers so I wondered if the cylinder thermostat was demanding heat from the boiler to reheat it to explain why the boiler was running - but why would the radiators still be on? So I turned down the cylinder stat and everything shut down AND the radiators went cool. I then turned the cylinder stat back up, the boiler fired, and that radiators heated up!?

So the sequence of events is:

1. We moved into a new house, and didn't really know how the boiler worked so have never really known if it has EVER worked as it should. Although it WAS controllable by the room stat CM907 but I'm not sure if it worked INDEPENDENTLY from the 9100 (as it should)
2. Then we had some work on the house and the sparkys somehow made the control cable from the CM907 permanently live so the heating was permanently on. This was diagnosed by the Worcester man who said the boiler itself was fine.
3. Sparkys came back and seemed to sort the problem so that the heating was now not permanently on, the CM907 regained control of the boiler BUT only when the 9100 was also ON (when I contacted you guys!).
4. Boiler now seems to ignore CM907 AND 9100 and only "listens" to the cylinder stat. So that if the stat is set very low the boiler AND radiators switch off, but if it is set to 60C the boiler comes on (as it should) BUT SO DO THE RADIATORS!!??

Has there been some sort of valve failure on top of the original wiring prob?? Who should I call - the Worcester man is free (warranty!), the electricians will no doubt charge me for scratching their heads and not sorting it (like last time!)

 

[MattC76]

The plot thickens: when I put the 9100 into continuous mode, the CM907 regains control of the boiler and switches it on and off according to the target temp!

 

[tamz]

You need a decent heating guy to sort it out for you. One who understands wiring (not all do). Electricians rarely understand heating controls so it can take them a while to figure things out and they won't know if it is working exactly as it should.
The Worcester engineer would (should) be able to tell you exactly what is wrong but they will charge you as it is a controls / wiring problem and nothing to do with the boiler or warranty.

 

[sparkygas]

All of the above could be true, but on my patch i see this mostly when a new conventional is installed onto an old three wire three port valve existing install, that is wired in hot water priority, ie the cylinder stat satisfied terminal livens up the room stat common, which is wired back to the boiler switched live. Crazy but true. Best bet is to get a good sparks who knows what a W Plan system is to come and test the system out. Hope this helps Matt

 

[MattC76]

Hi - tamz / sparky thanks for the replies.
The reason I suggested getting the Worcester guy back out was that when he originally came (under warranty) he did a lot of fiddling with the wiring i.e. disconnecting/reconnecting etc to find a diagnosis so it is feasible that he reconnected things incorrectly. Would the warranty cover putting a "non-boiler thing" that the Worcester engineer caused?

I'll also try and dig out the people who originally installed the system.
Matt

 

[tamz]

The problem with getting worcester back is the engineer fiddled with your wiring off his own bat which was not part of his work requirements so worcester will not send someone to fix that as it was not authorised work.

Maybe best get hold of the original installers or a heating guy (or a spark who understands heating :smile and get it sorted out.

 

[sparkygas]

I'm really surprised he did any 'fiddling' external to the boiler under warranty, his bosses would be appalled... Chances are the guys who installed it don't understand the old valve/wiring configuration either, hopefully they know a man who does. Sorry to be negative but in my job as a QC for a large heating firm I come across it often.

 

[MattC76]

So how much do you reckon a heating guy would charge to sort it assuming its a "simple" wiring problem?

Also on a slightly different topic, I have read that the rad (in the hall) where the room stat is should not have a TRV and should be fully on? The problem is then that the hall heats up very quickly and the stat turns the boiler off before the other rooms have heated up?!! The logical thing to do would be to turn the hall rad down a bit so the hall doesn't heat up too quickly - but is that ok?
Cheers,
Matt

 

[tamz]

Someone would need to have a look and see exactly what was happening. It may take an hour or it may take 4 depending on what they actually see. I'll leave the costs to whoever sees it but it should be reasonable.

If your hall is small and heats quickly you may be best moving the stat but it could just be set a bit higher in the meantime to allow the rest of the house to get up to temperature. If you had a trv on the hall rad and turned it down then the room stat would never get up to its set temperature.

 

[dancinplumba]

could try reducing flow through rad with lockshield and take off trv head

 

[Toned.f]

Hi - tamz / sparky thanks for the replies.
The reason I suggested getting the Worcester guy back out was that when he originally came (under warranty) he did a lot of fiddling with the wiring i.e. disconnecting/reconnecting etc to find a diagnosis so it is feasible that he reconnected things incorrectly. Would the warranty cover putting a "non-boiler thing" that the Worcester engineer caused?

Yeah right

 

[MattC76]

Yeah right

What d'you mean?

 

[tamz]

He means Worcester won't fix it.

 

[MattC76]

Hmmm I was afraid of that! I'll get someone in - thank you all for your help / advice. I'll let you know what happens.
Matt

 

[billybob150811]

good luck you want some one who will spend x amount of hours belling out and who might say dust on the contacters £200 please people are very reluctant to pay for fault tracing consider buying some new gear it maybe cheaper to rip out and start again not what people want to hear and just a view you can consider or dismiss

 

[Billy Bob Bob]

sounds like you have a fault/wiring issue with your system,also sounds like the worcester guy went above and beyond to try to help you but now your pointing the finger and blaming him for his helpfulness,he did not have to help you he could have said its not a product problem sir and a big bill would have been sent your way,instead he tried to sort your problem,but you sir can not see this,get a engineer in,but recognize the fact someones tried to help you,people like this a very few and far between

 

[MattC76]

sounds like you have a fault/wiring issue with your system,also sounds like the worcester guy went above and beyond to try to help you but now your pointing the finger and blaming him for his helpfulness,he did not have to help you he could have said its not a product problem sir and a big bill would have been sent your way,instead he tried to sort your problem,but you sir can not see this,get a engineer in,but recognize the fact someones tried to help you,people like this a very few and far between

Hi Gasman - I am not blaming the Worcester engineer and am certainly not pointing any fingers at anyone. I merely raised the possibility that he COULD have rewired it incorrectly after diagnosing that it was an electrical problem and if that was the case then if it would be reasonable to get him back and sort it. However it seems from all the other helpful responses that this would not be reasonable so I'm going to get an engineer in. The original engineer was an absolute legend and very helpful and clearly loved his job.

 

[Toned.f]

sounds like you have a fault/wiring issue with your system,also sounds like the worcester guy went above and beyond to try to help you but now your pointing the finger and blaming him for his helpfulness,he did not have to help you he could have said its not a product problem sir and a big bill would have been sent your way,instead he tried to sort your problem,but you sir can not see this,get a engineer in,but recognize the fact someones tried to help you,people like this a very few and far between

Ditto

 

[MattC76]

Can I just reiterate that I really am not blaming anyone for this especially the Worcester engineer - he did not have to go the extra mile to diagnose the problem and I am very grateful to him - he has no doubt saved a lot of time, trouble and expense for me...I just wondered if he had wired it back wrong - which I think is potentially feasible and IF that was the case whether he would sort it out - which I now understand would not be reasonable of me to expect. I did not know that the controls/wiring was not part of his remit - if I had known I would have not suggested getting him back!
I am not pointing any fingers! I just want advice which is what I've got so thank you very much!
Cheers