Moonshine Posted December 7, 2019 Share Posted December 7, 2019 This may not fit the remit of the forum as it's a question about an existing boiler which is exhibiting a fault or sorts, which I am questioningy sanity about. The boiler fires normally on request, it heats hot water and central heating up to a point and then shuts off as a normally should once it's reached temperature. However it seems not to want to turn on again automatically, once the water temperature in the radiators has dropped. The central heating pump is still pumping water around the system but it's just colder water the boiler doesn't seem to recognise needs to be heated. When the boiler is turned off and on again, it then recognises the water needs to be heated and starts heating the central heating again. Can anyone give any indication of what could be wrong with it or am I doing something silly. Cheers Link to comment Share on other sites More sharing options...
Temp Posted December 7, 2019 Share Posted December 7, 2019 (edited) More info on the system required. Any error messages/numbers on the boiler or no display? Possibly the water temperature sensor in the boiler. Could also be switch contacts on a diverter valve not passing on the signal to fire the boiler? Edited December 7, 2019 by Temp Link to comment Share on other sites More sharing options...
Moonshine Posted December 7, 2019 Author Share Posted December 7, 2019 1 hour ago, Temp said: More info on the system required. Any error messages/numbers on the boiler or no display? Possibly the water temperature sensor in the boiler. Could also be switch contacts on a diverter valve not passing on the signal to fire the boiler? Cheers, it's an older glow worm Ultimate 40FF. No display at all and no fault codes. Any way of diagnosis which one it may be? Interesting I have the CH on now (without the hot water on), and has been on a while. The radiators are hot and the boiler is lighting and turning off in approximately 2 min intervals, then restarting again fine, until it turns off after a couple of minutes. The over headlt cut off button doesn't pop out. Link to comment Share on other sites More sharing options...
Temp Posted December 8, 2019 Share Posted December 8, 2019 This thread sounds similar. Turned out to be the temperature sensor/thermocouple.. https://www.diynot.com/diy/threads/glow-worm-boiler-not-firing-up-update-now-fixed.246017/ Link to comment Share on other sites More sharing options...
Moonshine Posted December 8, 2019 Author Share Posted December 8, 2019 8 hours ago, Temp said: This thread sounds similar. Turned out to be the temperature sensor/thermocouple. Thanks I will take a look and see if there are similarities Link to comment Share on other sites More sharing options...
Moonshine Posted December 9, 2019 Author Share Posted December 9, 2019 so with a bit of testing this weekend it looks as though it is an issue with the interaction with the hot water and CH. When the CH is on in isolation (and the hot water hasn't been on), then the CH works as it should, switching on and off, keeping the radiators nice and hot. however when the hot water is on, and has got hot enough, its like the boiler doesn't recognise a need to keep the central heating water hot, it just mindlessly pumps water round the CH system getting colder and colder. So when all is off and starting from cold and both the CH and HW are turned on, the boiler gets the radiators warm, and when that is up to temp, it switches to heating the water in the tank. When the tanks up to temperature it should switch back to the CH, and keep that temp topped up. However it seems that it switches back to the CH, but the boiler doesn't fire. Its like that as long as there is hot water in the tank it doesn't need to fire back up. This seems more like an issue with the diverter valve and switching, what would be the diagnostic fault test on this element? Link to comment Share on other sites More sharing options...
Temp Posted December 10, 2019 Share Posted December 10, 2019 On 09/12/2019 at 16:33, Moonshine said: This seems more like an issue with the diverter valve and switching, what would be the diagnostic fault test on this element? Are you happy working on live electrics? The manual here.. https://www.plumbase.co.uk/documents/product/3548621 Has likely wiring diagram bottom of page 21. I would have a look at the voltage on Switched Live (SL) with respect to N. Think that should be 240V whenever the stats (DHW or CH) are calling for heat. See if it's live when it should be. If not then the problem is in the wiring rather than the boiler. On some systems the signal from the stat moves the diverter valve and switch contacts on diverter turns on the boiler when the valve has moved to the required position. So there could be a short delay between a stat calling for heat and SL going live if the signal is routed through contacts on the diverter. These contacts on the diverter are a common source of problems especially if the valve weeps. If the diverter moves but SL never goes live that would be a good place to look. On an old system I once had the switch contacts could be removed and inspected/cleaned but better to replace them. Make sure system power is off before working on these. I like to remove the fuse. If SL is live when expected and the boiler still isn't firing up then problem is in the boiler. 1 Link to comment Share on other sites More sharing options...
bmt216a Posted December 11, 2019 Share Posted December 11, 2019 If it’s a mid position valve (y plan) if there is a heating demand, you should get 230v on the white wire. However If the pump is constantly running but the boiler isn’t firing, you might have an issue with the boiler as the pump runs with a demand. 1 Link to comment Share on other sites More sharing options...
Moonshine Posted December 11, 2019 Author Share Posted December 11, 2019 Thanks for that manual, and it has a useful fault finding page. Opening up the casing with all turned off, then turning off indicates that neon 1 and 2 are lit. Testing as per the fault finding finds no 240v between n/c on air pressure switch and N. Which means it needs a new PCB according to the fault guide. Oh well... Link to comment Share on other sites More sharing options...
Moonshine Posted December 11, 2019 Author Share Posted December 11, 2019 (edited) Oh FFS! I have put it all back together, cover on and turned on at the isolator. And low and behold the thing fires up no questions asked. Looking like a temporary fix but seems the PCB is on the way out. Edited December 11, 2019 by Moonshine Link to comment Share on other sites More sharing options...
Ed Davies Posted December 11, 2019 Share Posted December 11, 2019 2 hours ago, Moonshine said: Looking like a temporary fix but seems the PCB is on the way out. In my limited experience electronics either works or it doesn't [¹]. Intermittent faults are usually mechanical things like connectors. With any luck you've jogged something like that which will now work happily for ages but if it does fail again try reseating the connectors if possible. [¹] after you turn it off and turn it on again if there's any software involved. 2 Link to comment Share on other sites More sharing options...
Temp Posted December 12, 2019 Share Posted December 12, 2019 (edited) I hesitate to post this as you probably need to be gas Safe registered to work on a boiler. Refurbished Main PCBs appear to be £35 or £60 depending on ??? on eBay. https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F332386761691 https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F332386777784 Not sure what difference there is. Edited December 12, 2019 by Temp 1 Link to comment Share on other sites More sharing options...
Moonshine Posted December 12, 2019 Author Share Posted December 12, 2019 (edited) Cheers for those, I will probably source the refurb PCB (visually and codes it looks the same) and get a gas Safe engineer I know to fit it. Edited December 12, 2019 by Moonshine Link to comment Share on other sites More sharing options...
Nickfromwales Posted December 12, 2019 Share Posted December 12, 2019 GSR’d fitter required if the case you have to remove to get access to the duff part forms part of the air / flue / combustion chamber. Look for any notes in the MI’s that state any disturbed seals need to be replaced. I would concur that it’s a PCB fault as it sounds like a relay has gone grotty and is allowing voltage through when energised but not when in the ‘normal’ state. 1 Link to comment Share on other sites More sharing options...
Moonshine Posted December 13, 2019 Author Share Posted December 13, 2019 Refurbished PCB installed and boiler now working as expected. Good to have a warm house again!!! Link to comment Share on other sites More sharing options...
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