Central heating & boiler problems ! HELP

Ok first of all i probably wont have enough info for you but you may still be able to help,I have a baxi boiler not combi! (not sure what model as im at work) late 90s model if that helps.

The problem i have is when i have both the central heating and the hot water on,the radiators will heat up as will the water even though the thermostat in the house says it should be off,so what i get is the radiators carrying on getting hotter and hotter, but if i have just the central heating on the thermostat will work fine and turns the central heating off automatically.I only get this problem when both hot water and central heating are on together.

I have changed both the zone valves and thermostat on the cylinder due to old age so i know there ok anybody have any ideas ?

So you have 2 2port valves, which are both new?
When the HW is on, check the CH one is actually closed.
Is there a radiator in say the bathroom which gets hot when HW alone is on?
Has it always done it, and do ALL the rads keep heating?

ChrisR said:

So you have 2 2port valves, which are both new?
When the HW is on, check the CH one is actually closed.
Is there a radiator in say the bathroom which gets hot when HW alone is on?
Has it always done it, and do ALL the rads keep heating?

Click to expand...

HI chris i have one new complete valve on hw and a new motor only on the ch, i'm pretty sure the ch valve is closed when this is happening.all the rads get hot, but i will check this out tonight.i believe i have always had this problem but did'nt really notice, because when the hw gets up to temp it switches it self off, then the house thermostat for the ch will take over.and if up to temp it will all go off.
It's strange but it seems like the hw just overides the system!

Hi Chris, just to let you know, all the rads come on with the hw turned on, and the ch is turned off at the control box!i believe there are flow and return pipes coming out of the boiler?and the ch valve is on one off these pipes, it is in the closed position when the hw is on yet still seems to have water flowing through it! yet when the hw water is turned off and ch is on, the valve will open and start the pump, hence starting the boiler.I'm starting to think that there should be another valve some where on the system to stop the ch when the hw is on, because the valve on the return or flow pipe does'nt stop the ch when the hw only supposed to come on!
Sounds complicated i know but it's probably something simple.And yes i think it has alway's done it.


Cheers Chris hope you can shed some light!!!

by the way the boiler is a

Baxi solo 2 40 pf