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I've got a 15-20 year old boiler that has been working fine since we moved in a few years ago. I've just tried turning on heating only this morning and it didn't fire up...
When I switch hot water only the boiler fires up and works fine (and warms up water in the cylinder).
When I switch hot water and heating the boiler fires up and we have heating and hot water
When I switch only heating it won't fire up at all.
I've turned the thermostat up to full and this makes no difference. I've also tried turning off the power supply to the boiler and the diverter valve thing that seems to power the thermostat and switch (and turned it back on again). It's not a huge issue at present but would rather not have to warm up hot water every time I want the radiators on.
Is it time to call the plumber or are there a few simple things I could try myself?
Thanks in advance.
Dave
Sounds like the boiler itself is fine - it's just not getting a signal to fire for heating demand. Sounds like the problem is the thermostat or the central heating controller.
Most likely a motorised valve issue.
Must be a 3 port valve, if you can, change the motor in it. Pick them up for between £10-20, simple only 2 wires to deal with and most of them come with a connector you can use.
Be aware not all valves have motors that you can change though.
Of course if you know how to use a multimeter you could check where the signal is being lost, but as you say if you select both you get heating then clock and stat would appear to be working.
Thats weird .
It wont fire when switched to CH only, but works fine on HW . I am guessing its not a combi , but trad system with HWT in an airing cupboard.
Dont think it will be the diverter valve, but it might be .
Sounds more like a signal issue from the thermostat / other control gremlin .
I had these exact same symptoms recently and it was the thermostat.
Thanks for the comments so far. Do I need an electrician then?
Tia, Dave
Plumber will be able to do thermostats. If you're comfortable with electrics you could replace the thermostat itself, ideally first wiring it directly to the controller to eliminate all the wiring.
You can do a thermostat yourself, its easy and cheap so you may as well do it just to rule out that as a cause. My thermostat is an electronic one, a replacement was about £15 from Screfix. Installation is easy, no need to shut the power down if the timer is not on...the thermostat is only live when the timer is on...well it is with my setup anyway, so no need to even shut the power down. Most thermostats have the same wiring layout so installation is straight forward anyway but obviously try to get the same type to make it even easier.
Before you go spending money on a thermostat is best to check exactly what the problem is. No-one's going to be able to correctly diagnose over the internet, your best bet is either getting a heating engineer in or if you feel up to it checking yourself - there are plenty of guides online.
Off the top of my head it could be:
Faulty 3-way valve
Thermostat
Wiring problem
Faulty programmer
i do think the money spent on parts darts would be better spent on a cheap multimeter and follow some youtube vids on tracing so you can find the faulty part and replace that ......
Well my point was that the cost of getting an electrician in to diagnose the thermostat is many times more than replacing the thermostat so you might as well go ahead and replace it. circa £15 vs £60+. If it works then you're quids in...if not then you can always get an electrician in and you know that the thermostat is not the issue.
These systems are not rocket science. There are differences from system to system and half the battle is understanding how your system works...but an electrician you get in will have that same problem, but it is not beyond the capabilities of anyone to spend a small amount of time and effort understanding how their system works and systematically testing the individual elements.
It is unlikely to be a wiring problem unless the wiring has been disturbed through other work that may have gone on around the home, so that's easy to single out.
Motorised valves are easy to single out by manually latching the valve.
You know its not the boiler as it works with other parts of the system.
You'll know right away if the programmer is faulty, so an easy one to rule out...and again another easy fix for someone with little or no DIY skills.
So if not the boiler, wiring, motorised valve or timer then it has to be the thermostat, which is tricky to test so just replace...cheaper than buying tools to test it.
So you should be able to rule out all of these elements either way quickly and simply. Once you've done that there really is nothing much more to test so then is the time to start spending more significant amounts of cash on getting an electrician in.
It’s what Bear said. The micro switch isn’t activating in CH. the valve is moving to Ch but not firing the boiler. It will work in CH and HW mode as the boiler is firing from the cyclinder stat.
Easy to change the motor as he said.
10 quid on a multimeter wont be wasted and learning how to use it is never time wasted. Such a handy tool
replacing the thermostat just because its easy might well be wasted time and money.
a multimeter will diagnose each part of the system working or not working when used correctly - basically identify inputs and outputs of the componant. Modify the input and monitor the input/output when you demand change of state
Change the part that isnt working.
plenty of youtube videos showing how.
Yes you will spend a 10er on tools (ok it wont be the greatest or the most accurate but your tracing change not exact values here) but youll not spend 15 quid changing this , didnt work - 20 quid changing that valve - it didnt work ..... then you change the other valve oh and it worked.
Wasted time and money.
From experience I change dozens of synchron motors every year and very few thermostats. If you are going to guess the part go with the motor. If you want multimeter will confirm which one but unless you are competent in heating controls and wiring then you could just confuse yourself
Thermostats are easy to prove as are programmers.
Some electricians are good on heating wiring but in my experience most aren’t.
Good luck!
Motorised valve unit changed, problem solved. Thanks all for your comments.
I like the thread and I like the feedback. Thanks for letting us know what happened.