[Closed] issue with CH and hot water!

have you tried turning it off and turning it back on again?

sounds like the diverter valve is stuck/passing

sounds like a motorized valve has gone.. could be wrong though.

Yep, diverter/motorised/3 way valve has most likely gone.

Edit, it's a valve that controls wether the hot water from the boiler gets pumped through the hot water tank or round to the radiators. They can fail or stick which leads to exactly what you're seeing. I think some of them have a manual option (switch) but not sure and I'm not a plumber so don't try anything on my say so 🙂

TRVs stuck too?

Not the trv's. As above, almost certainly the 3 port valve. Should cost between £180 - £250 to replace. If it's a Honeywell, you might be able to replace only the motor.

ALL of them even the ones that are set to off on the TRV's

Not sure what you mean cynical. 🙂 The TRVs aren't the issue here. The problem is that the rads are getting hot although there is no heating demand. When the hot water cylinder is calling for heat the rads are also heating up. The most likely explanation for this is as above.
If there was a problem with TRVs it would be completely independent of the issue the op has described and would need to be dealt with after this problem is first resolved. Also, highly unlikely that every TRV would be faulty.

Gears - he means if the TRV's are off how are the rads getting hot? It would imply that ALL the TRV's that are off are faulty too.

the 2/3 port valve is at fault. the trvs are most likely on a snow flake setting allowing a small amount of water through to keep circulation. i would NOT reccomend closing fully any rad valve as restating circulation when you want that or any other rad on can be a real pain so no more 'off' than snowflake pls folks..

My TRVs don't have an 'Off' position - when turned all the way down, the temperature they come on is lower - about 15º from memory. It would be useful to know what temp the OP's house is at when they are coming on, to see if there is a problem with them. But the main problem will almost certainly be the 3 way diverter.

Non of this is helping the op. We could discuss trv's all day long. Evidently, we all know how they work. Once again, the problem is most likely as above.

Is it a proper job or a DIY job?

If it's a Honeywell Y plan valve they are notorious for developing problems after a few years. I'm having a battle with Honeywell right now over my second valve in seven years.

I had this problem a couple of months ago with our Worchester Bosch oil fired combi. Changed the diverter valve and all was good again.
It cost £70 for a genuine part from a local plumb center. 5 mins max to change over (turn off the electric first!) and 1/2 hr to test properly.
When I took the old one apart the lugs that the internal springs attach to had both broken.
Look up the schematic for your boiler to work out if you can do this yourself. If you're not confident after a bit of research get a pro in.

thetallpaul. What colour is the sky in your world?
A. not talking about combi's
B. no diverter valve in op's boiler.

gears_suck,
No need to be abusive, I was just trying to help.

Bad morning?

The boiler is an icos he12 if that means anything to anyone! If it is a valve does the system need to be drained prior to doing anything??

thetallpaul. 'Twas only a joke. Don't take offence.
The boiler in this case is not relevant. Draining down is generally required in order to change the whole valve, but not to replace the head alone. At this point, based on your questions, I recommend calling a heating engineer/plumber. If you know a good one or can get a recommendation it will be money well spent.
Edit: reading my previous comment again. It does sound a bit offensive. Apologies for that tallpaul. No, not a bad morning. I'm just generally a bit of an asshole.