Combi Boiler providing hot water but no heating?

[TomEC]

Morning all,

I have a problem with my Baxi Combi 105 HE boiler. I think I know what the problem is but I'd really like to run it by some more knowledgeable folk before I commit to it.

There is always plentiful hot water, but the radiators do not come on. The hot water demand light is always on, the radiator demand light is never on. I have a short term fix for this, which is as follows: Whilst looking at the indicator lights on the panel, I run the hot water tap and watch the red, temperature indicator lights start to go out. When 2 or 3 of the lights have gone out and the flame light comes on I turn the hot water tap off and, lo and behold, the radiator demand light comes on and the heating comes on.

It is my belief that this is caused by a dodgy diverter valve. My plan is to buy a diverter valve servicing kit, remove the valve, service and clean it, and replace it.

Does this sound like a sensible diagnosis and solution? Is this likely to solve the problem? Is there anything else that could be causing this problem?

(Also is this a particularly difficult thing to do? I am not a plumber or heating engineer, but I am generally pretty handy. I'm an electrical/electronic design engineer and I build a lot of prototype equipment, I do my own electrics and minor plumbing work and any random bits of DIY around the house.)

 

[Theweeknd]

How do you control your central heating ?

It could be a dodgy room thermostat.

 

[TomEC]

I have a remote control thermostat, but that seems fine. When I do the trick with the running water, the temp control on the thermostat seems to work fine

 

[Theweeknd]

I have a remote control thermostat, but that seems fine. When I do the trick with the running water, the temp control on the thermostat seems to work fine

But the remote control thermostat should be providing the demand to the boiler.

Have you changed the batteries ?

 

[TomEC]

I haven't, no, and I will give that a try, but I don't think that's the problem. The heating starts and stops working based on the flow of hot water, with no change to the operation of the thermostat. I would expect that if the thermostat was failing to communicate with the boiler, then the heating would stay off regardless of what I did with the hot water taps.

Still, it's a cheap fix to try, so I will swap them out and see what happens

 

[ianmcd]

remove the front cover and on the bottom left hand side you will see the diverter valve, on the large diaphragm housing at the front, there is a micr-switch that tells the boiler that a hot tap is running, make sure the pin is retracting properly when the hot tap is closed, and that the micro switch is breaking.

 

[TomEC]

Thanks Ian, I'm at work now but I'll take a look at that this evening. If the pin is not retracting properly is that indicative of a faulty diverter valve? In this case should it be cleaned/serviced or replaced?

Thanks
Tom

 

[ianmcd]

Thanks Ian, I'm at work now but I'll take a look at that this evening. If the pin is not retracting properly is that indicative of a faulty diverter valve? In this case should it be cleaned/serviced or replaced?

Thanks
Tom

yes it can be, can also be caused by a dripping HW tap or a leak, if the pin is indeed sticking, isolate the cold water inlet under the boiler, if the pin still sticks the DV needs servicing, if it now retracts with the cold water isolated it is a leak or a dripping tap