Right boiler specialists, what’s happening here? Central heating is off, boiler is switched on, yet the radiators are warm. Is there any way that the heating can be heated up by the hot water side? The pump doesn’t come on, and the burner doesn’t fire, except under hot water demand. I’m off to the pub, shall expect a solution in the am. Don’t let me down.

check your wall cavities … for the bones of witches

Mine dumps excess heat from the hot water side onto the radiators. The one closest to the boiler will get warm after running hot water for a while.

We used to have a boiler in an outside cupboard, and it had a frost thermostat in the cupboard, so the boiler would fire up if it got REALLY cold.

When the boiler was serviced once, the service chap obviously tested it, and adjusted the froststat so that it kicked in at a much higher temp (i.e. the ambient temp), so the boiler acted as if it was freezing and fired up all the time.

Some of the same symptoms as you’re seeing, but obviously the boiler was firing up. Are you sure yours isn’t? Difficult to see how else the rads are getting warm…

Disgusting. Reported for smutty overtones

You can also get convective circulation, especially if you have vertical runs of pipe near the boiler.

To counteract that, you can get the fantastically named “anti-gravity valve” – a decent plumbers’ merchant will know what you mean.

What jambo says, if hot water is run the boiler will dump some heat to the heating system to prevent it overheating.

Or the diverter is passing into the heating side, or the plate heat ex is knackered.

To counteract that, you can get the fantastically named “anti-gravity valve” – a decent plumbers’ merchant will know what you mean.

😆 We keep ours next to the tartan paint and long stands

Could be the three way switch thingy ( I’m not a plumber! ) had one in my old house when putting hot water on the rads would heat up. Do you have an old boiler and hot water tank? Valve stuck open so water in tank is heading to radiator s?

Can’t remember what is called but with the older boilers you will find a diverter box valve thing near the cylinder, often with a visible lever to manually switch it. If this gets stuck it can’t switch between hot water only, or hot water and heating. Also there is a fault condition where the water circuit can overheat and hot water gets sent back to the cold water tank in the loft which can be a bit dodgy as the tank softens up!

Three way switch here too.

There’s often a manual override, try that a few times to see if it helps.

The switch was my first thought.

Your post implies a combi. These have a 3 port diverter valve inside which will “divert” to hot water when there is demand for hot water but goes back to central heating if demand is there for heating.

My guess is the valve is knackered, causing convection round the central heating when there is a call for hot water.

Rich.

Flux capacitor at warp drive is overheating. Call Scotty.

Thanks all, yes should have said it’s a combi, ideal isar, fitted for the previous occupant under the warm front scheme. Also, last time I switched the boiler off to change a rad, it started leaking near the plate heat exchanger…

Ahh, Ideal Isar. Best place for that is the bin.

Chances are it’s the diverter valve cartridge but make sure you get the right type as there’s 3 different options. If it’s a Honeywell grey box actuator I may have a cartridge you can have for postage, need to rummage in my drawer of doom at work to make sure though.

Great stuff men of Stw I knew I could rely on you, we bought the house 2 years ago, hopefully this boiler will limp on for another year,until we get to to that floor, done 2 floors so far another 2 to go, but may have to get to the boiler before that…..luckily I have another same model I can scavenge for parts.
Okay just had a Google and all I can say is thank god I’m not paying someone. Please work for another year. Thanks for replies chaps