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Central heating issue (but not on boat)


starman

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7 minutes ago, starman said:

Maybe there's a clue in the fact that the 'heating thermostat' on the boiler doesn't click any more but that might be a fault elsewhere of course.

 

Do you mean the temperature control knob on the front of the boiler, or something else? If that isn't clicking, it probably just means the boiler is already hot, so it is not calling for heat and won't, no matter how high you turn it. To be expected if the pump isn't pumping away the hot water.

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1 minute ago, Mike the Boilerman said:

 

Do you mean the temperature control knob on the front of the boiler, or something else? If that isn't clicking, it probably just means the boiler is already hot, so it is not calling for heat and won't, no matter how high you turn it. To be expected if the pump isn't pumping away the hot water.

Ah, of course - now I know why I'm not a heating engineer!

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Its colder this morning  so how is the room stat set? (Not the boiler stat). The room stat usually controls the  central heating circulating pump so if its set too cold the boiler will do exactly as you say until you turn the room stat up. Also circulation pumps have, in my experience, a habit of jambing over the summer so sometimes a clout with a lump of wood frees them off, probably much like your turning the thing on and off.

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13 minutes ago, Tony Brooks said:

Its colder this morning  so how is the room stat set? (Not the boiler stat). The room stat usually controls the  central heating circulating pump so if its set too cold the boiler will do exactly as you say until you turn the room stat up. Also circulation pumps have, in my experience, a habit of jambing over the summer so sometimes a clout with a lump of wood frees them off, probably much like your turning the thing on and off.

Hi Tony. No room stat on our system just thermostatic rad valves.

I have done the first two diagnostic tests - switch off and on again, then hit with hammer ?

These oil boilers are a PITA (unless you're a boilerman) but to be fair ours does need a service so if I can keep it going for a few days with the off-on technique then the repair man should be able to sort it.

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16 minutes ago, Tony Brooks said:

I hate combi-boilers and will avoid a condensing boiler for as long as I can. Both, in my view, overly complicated and in the case of combis easier to install at the expense of reliability.

 

Ok back now. 

 

Totally agree with the above. 

 

 

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Just now, plainsman said:

Some CH systems have a motorized valve to separate the heating circuit from hot water.  These can stick/break

 

The OP has narrowed the fault down to the CH pump not running. This boiler has two pumps (unusually). One for CH, one for DHW. 

 

We need to focus on why the pump doesn't run, not make wild guesses.  

 

 

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22 minutes ago, Tony Brooks said:

I hate combi-boilers and will avoid a condensing boiler for as long as I can. Both, in my view, overly complicated and in the case of combis easier to install at the expense of reliability.

I hate combis too - ours has had endless problems; the electronic stuff all gives up at about the same age. I think they're a poor concept too - often they can't provide enough hot water for a house and usually located where you waste large amounts of water running a tap before hot arrives.

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Just thoughts pondering the system

 

If there really is no room stat then the heating circulation pump would keep heating the pipes and this strikes me as not very efficient so the circulation pump would have to be controlled by a boiler stat.  But if so when the TVRs on the rads were closed it could not circulate water UNLESS either one rad or towel rail has no TVR or the system is equipped with some kind of bypass valve. In the latter case  bypass valve jammed shut would give the symptoms and in the former it would be wise to check no one has turned a manual radiator valve off.

 

I think one of the electric valve on my conventional system has a lever on it with a latch that you can fix in the open position, maybe worth a close look but in my case I do not think its a bypass valve.

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As an oil boiler technician, I see a lot of these. The CH pump will not run unless the heatstore is up to temperature, and the electronics tell the PCB so.

First test is to check the outputs at the terminal box. Remove the cover and you have arrow of connectors. Firstly, establish your command currents. Secondly, check the pump outputs. If you have 230 at the CH pump outlet, the pump is goosed. If you don't, do you have 230 at the DHW output. If you do, and the water is hot, take the sensor out of the heatstore and clean it. Also make sure the heatstore is properly vented; a sensor will not sense if the pocket is in air. If this does not cure it,try swapping the temperature sensors over. These thermistors are quite a common failure. If this makes no difference, then the DHW PCB is probably goosed.

Edited by Ex Brummie
There are two temperature PCB's, one for DHW and one for CH.
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I have one of these boilers (remember - the 24v relay etc) - and I have not been terribly impressed.  It has proved difficult to locate precisely the correct manual- even the one that came with it is not 100% representative.

 

The redeeming feature is that it is quite simple.  The electrical side looks like it has been assembled from a 1970s Junior Electronic kit.   I can find a circuit diagram, if it helps.

 

From my experience, I would first be checking that volts were arriving at the CH pump - and taking a peep inside to see if the capacitor was cooked.   I also had a PCB  go.  On my boiler, there were two PCBs - essentially one for the hot water and one for the heating.  One (heating?) has a rheostat knob poking through the panel  - but when you look carefully, the other one has the same spindle - but hidden away.  The point being that the PCBs are the same - and if you are getting no output to the burner and relevant pump from one, you can swap it over to see if you the issue  changes to the other side.   About £50 online.

 

I don't like combi boilers either.  The output was slow and barely hot enough.  So I installed a copper cylinder and three port valve, and now heat via the CH side.  The hot water is stopped off, but if I can remember just what to do, can be reconnected by operating a few valves and stopping-off the expansion pipe.  It is much better - plenty of hot water.  I'd like to have a header tank rather than the pressurised system - but I don't think I can generate the 1 bar it desires.

 

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10 hours ago, Mike the Boilerman said:

 

The OP has narrowed the fault down to the CH pump not running. This boiler has two pumps (unusually). One for CH, one for DHW. 

 

We need to focus on why the pump doesn't run, not make wild guesses.  

 

 

I bow to your knowledge and  consider myself appropriately  chastised 

  • Haha 1
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8 hours ago, Ex Brummie said:

As an oil boiler technician, I see a lot of these. The CH pump will not run unless the heatstore is up to temperature, and the electronics tell the PCB so.

 

I didn't realise it is a storage combi. If it is, then yes I agree with your observation, this is how they work usually. 

 

It is not consistent with the heating working if the the boiler is re-started though, as the OP says happens. The store temp does not change when the power is turned off and on again.

 

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Well very strangely the ch started itself up and is running fine this morning!

Who knows why - maybe all the repeated stop-starting yesterday, I cleaned the probe too and (my illogical theory) checked pump volts which involved fiddling into a sort of Wago block of connectors - maybe one was a bit dirty. 

Anyway it’s working so thanks for all the advice but I suspect I’ll  be back!

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Glad its working.

 

The diagram for an Outdoor Combi 90V3 (it covers various sub models) is below.

Outdoor-Combi-90-V3-Combi-Max-and-Outdoor-Vortex-Combi-26-and-36-installation-and-servicing-manual-DOC58-Rev01-March-2006_Page_47.jpg.fbdc4aecfdeec0d85795040106c19ea4.jpg  

 

Assuming your boiler is along the same lines, when it next goes wrong (it will) you could check for the CH side

  • That the permanent live is reaching  the boiler (big black plug)
  • The switched live is calling for CH (the big black plug - or terminal A1 on the first relay)
  • The switched live is reaching the live terminal on the PCB
  • The  PCB is outputting burner live
  • The burner live is reaching the burner and CH pump

And a picture for those that admire tidy wiring

 

1363606692_141205BoilerPCB(3).JPG.af434a7c047a0ea66f69ba2b5256eed4.JPG 

 

 

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6 minutes ago, Tacet said:

Glad its working.

 

The diagram for an Outdoor Combi 90V3 (it covers various sub models) is below.

Outdoor-Combi-90-V3-Combi-Max-and-Outdoor-Vortex-Combi-26-and-36-installation-and-servicing-manual-DOC58-Rev01-March-2006_Page_47.jpg.fbdc4aecfdeec0d85795040106c19ea4.jpg  

 

Assuming your boiler is along the same lines, when it next goes wrong (it will) you could check for the CH side

  • That the permanent live is reaching  the boiler (big black plug)
  • The switched live is calling for CH (the big black plug - or terminal A1 on the first relay)
  • The switched live is reaching the live terminal on the PCB
  • The  PCB is outputting burner live
  • The burner live is reaching the burner and CH pump

And a picture for those that admire tidy wiring

 

1363606692_141205BoilerPCB(3).JPG.af434a7c047a0ea66f69ba2b5256eed4.JPG 

 

 

Thanks for that - I’m sure it will go wrong again (probably the day before Christmas). Fortunately we have a wood stove. 

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Assuming the OP's boiler uses the same wiring as this outdoor model (highly probable) then the CH pump is fed with power from a relay. That relay in turn, gets its power from another relay which needs to be in 'relaxed' condition. That second relay operates during HW demand to starve the heating duirng HW demand. Given the intermittent nature of the problem I'd say either of those two relays is quite likely to be the culprit. 

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16 hours ago, Mike the Boilerman said:

 

I didn't realise it is a storage combi. If it is, then yes I agree with your observation, this is how they work usually. 

 

It is not consistent with the heating working if the the boiler is re-started though, as the OP says happens. The store temp does not change when the power is turned off and on again.

 

Mike, Not a storage combi as such, but all oil combi's have a slave tank,(or use the boiler itself as a slave). If there is a dicky sensor, turning off the appliance ( and hence the DHW pump) can let the latent heat build up sufficiently to tip the balance, or even shock a poor connection into life. All oil combi's give priority to DHW demand, and this includes heating up a slave tank. Some have a fixed DHW stat that you cannot easily override, which makes testing awkward after servicing.

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5 hours ago, Ex Brummie said:

Mike, Not a storage combi as such, but all oil combi's have a slave tank,(or use the boiler itself as a slave). If there is a dicky sensor, turning off the appliance ( and hence the DHW pump) can let the latent heat build up sufficiently to tip the balance, or even shock a poor connection into life. All oil combi's give priority to DHW demand, and this includes heating up a slave tank. Some have a fixed DHW stat that you cannot easily override, which makes testing awkward after servicing.

At last an expert to help out with the op's issue, pay no attention to the other advice it's obviously people who think they are experts but have little experience with oil combi's..

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  • 2 weeks later...
4 minutes ago, starman said:

Thanks for all the advice - the engineer came, fitted a new RD8 Riello photocell and all is now well.

 

Staggering! How on earth can a photocell have been causing the symptoms you originally described, I find myself wondering. Oil boilers can do mysterious things in my experience. Did the engineer give you any sort of explanation?

 

Thanks for the update, let us know if the problem re-surfaces. 

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1 minute ago, Mike the Boilerman said:

 

Staggering! How on earth can a photocell have been causing the symptoms you originally described, I find myself wondering. Oil boilers can do mysterious things in my experience. Did the engineer give you any sort of explanation?

 

Thanks for the update, let us know if the problem re-surfaces. 

Unfortunately I wasn't in when he came. I'm keeping my fingers crossed.

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I can see a situation where the photocell can have an effect on the O.P's problem.

The Riello RDB burner photocell is infamous for keeping a burner in prepurge where the uninitiated think the boiler is running. if DHW stat is in demand, then a purging burner will never satisfy it, and the CH pump will not run. Obviously, if the cell problem is intermittent, its full effect is not apparent to an inexperienced individual.

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