Central Heating weirdness

Obviously I will consult our plumber, but doubt he’s taking calls at 06:00

Last night the radiators were on, but only upstairs- but the heating wasn’t turned on. We are bit confused how this is possible? Especially as there is no way to only do upstairs or downstairs on our system.

Any ideas how this happened? Gas combi boiler, well maintained/ serviced. Think has happened once or twice before. Only thing I can think is was big jump in outside temperature yesterday,  but still not sure how/ why it would happen? Fixed having to turn boiler off overnight to avoid baking ourselves.

Cheers, Niall

Is your house haunted?

Are the downstairs radiator valves open? Are they trvs? If they are set lower than the room temp they will remain shut. Your upstairs trvs might be set high so the rads warmed up?

Is there a scheduled demand in your programmer that has decided to activate?

Why are my radiators hot when the heating is off?
There are a couple of system faults that could be causing your radiators to heat up when the heating is turned off. For example:

1. Diverter valve problem
If the diverter valve is broken or stuck in a combi boiler, it can cause your radiators to get hot when the heating is off. But how does it work?

When the boiler is turned on, the diverter valves control the direction of the hot water through the heating system. You can adjust the settings on the dial on the front of your boiler. The water can be directed to the radiators, hot water tap, or both.

The diverter valves open and close depending on the direction. So when you want to heat up your radiators, the tap diverter valve will close to allow hot water to head to the radiators instead of the taps.

To put it simply, the system works in the same way as a bath with a pair of taps and a showerhead attached where you can choose where the water comes from.

That will be £150 please for my googling skills call out fee 🙂

Sure thing, just give me your bank details, mother’s maiden name and password and I’ll sort that after school run.

Thanks for that @FunkyDunc

@retrorick – all valves working/ set ok as heating was on couple days ago worked fine. No scheduled demand set currently.

Have you got an immersion tank? Our 3 way valve fails about every 3 years and the radiators come on with the hot water.

Happened to ours, faulty diverter valve. Same hot radiators upstairs but downstairs cool.

An easy way to find out if it is the diverter valve is to run the hot water, see if it gets as hot as it normally does, and, go round and feel the pipes to the rads, starting at the boiler end. If the HW is colder, and the CH pipes are getting hot, then the diverter is failing. However, that should only happen when the hot water is running, the boiler shoudlnt come on on its own, which is how you described it.
The valves are not expensive, typically £50-100, many manufacturers sell a refurb kit which replaces all the internals in the valve for a lot less money.

all valves working/ set ok as heating was on couple days ago

1) This doesn’t even confirm that the fault didn’t exist a couple of days ago 🙂 I vote diverter/3way valve, I had the same. On my system the valve was outside the boiler on the pipe work and I was able to manually set it.

2) You had the heating on in June?!

3) Hot water probably only reaching the upstairs rads as ch pump not running/hot water rises, might even have travelled backwards around the loop.

Diverter valve, set it manually and replace it with one from screwfix

Sounds like diverter valve

I don’t think it’s quite so common these days with modern boilers but do you maybe have a single radiator upstairs that is plumbed separately from the normal CH loop? Used to be the case that there was a “special” radiator used to cool down the boiler after the demand for heating stopped – for a few minutes the boiler pump would continue to circulate round that single radiator to cool off the fluid in the boiler heating loop.

Does sound like a diverter valve issue – non-combi here, but radiators upstars came on when hot water was on. Only £25 for a new motor (Drayton Synchronus Motor on the pump)

“Does sound like a diverter valve issue – non-combi here, but radiators upstars came on when hot water was on. Only £25 for a new motor (Drayton Synchronus Motor on the pump) “

Combi boilers are totally different, in that the diverter valve is built in the boiler, and is model/make specific. They are quite different from external Y valves, but, essentially, do the same job. In a combi, they are diverter valves, set to run the CH at all times, unless there is a call for HW, in which case the CH is turned off while the HW is running. An external valve is usually a mid position valve. The difference is, the Diverter does CH or HW, a Y plan mid position valve can do CH, HW or both at the same time.