Help - does anyone know why my heating is on?

[bananamonkey]

I had the boiler serviced a few weeks ago, a bit of work was needed as the pressure kept dropping and we needed a new flue. Ever since I've noticed the radiators are sometimes warm. I've lived here 5 years so I know how to work the heating, the boiler is currently set to 0 for heating e.g. not on timer or constant and the thermostat is turned right down as far as it'll go which normally switches it off if it's on constant. Is there something obvious that I could switch/fix before resorting to calling out the engineer again?

if a combi, do they start to warm up when you run a hot tap?

Or if a cylinder, do they start to warm up when the HW timer comes on?

We had this and it was the same problem Piglet says - whenever the hot water came on, it filled the radiators too. Had to get a plumber around to change some switch.

I agree with Piglet - a couple of ours warm up when water is run.

Another problem we had one summer was when the c
frost thermostat went wrong and the heatinng came on - but in that case you would notice the boiler being on constantly.

It's a combo, I haven't made the connection with running the hot waster, I have noticed it most with the towel rail when I get out of the shower but I haven't made a point of checking it before, I'll try this tomorrow, thanks!

Sorry poor typing, I meant "combi" and "water"!

if it is, then the diverter valve in the boiler is most likely worn out and needs a pro to repair it. Commonly the radiators nearest the boiler warm up first.

It is possible to deliberately plumb a system so the towel rail (only) heats up during or after a bath or shower, which is nice, but this is not very common (mine does), and I have only known it done with a system that includes a HW cylinder.

Sorry to hijack but we are having the same problem- radiators come on when hot water comes on although thermostat is right down at 10 and heating switched off! However, ours is an oil fired boiler with a tank, not a combi. We have been told it is possibly the 3 port valve that controls hot water / heating - does this sound right?

yes.

So I've just tested it, definitely heated up after I had a shower, the towel rail doesn't have a separate control but the living room rads are also warm. Weird how it's only started happening after the servicing. Is it an expensive job? I'm still recovering from paying them £800 for a new flue

I have had this too, it is a faulty diverter valve.

I got a quote from two local plumbers who wanted £350 to fix it plus lead time to order the part.

I then went direct to the manufacturer who offered a fixed price repair for ~£180 and were able to fix it right away as they already had parts.

We had this when we move into a new build - since we moved in in November, we didn't notice until we turned the heating off in spring. It turned out that the guy who did the plumbing didn't know which way round to put the diverter valve so he put it one way in half the houses and the other way in the other half .

p.s.

the first sign of this happening is when your summer gas bill increases. For hot water only, you would normally use in the region of half to one cubic metre of gas a day, something like 20p to 40p plus standing charge.

Thanks all, really helpful advice. That is pricey Roses, we're moving out in a few weeks if everything goes well with our sale so have been trying to finish off little jobs.