Hot water only with CH

[mk2phil]

Wonder if you guys can help me...

I have a C plan system (pumped CH, gravity HW) with a Honeywell zone valve next to the HW tank.

Our programmer is set to call for HW and CH at roughly the same times. However, just recently what with the hot weather I've changed it to just call for HW - but now we dont get any. I've checked the zone valve when the HW is called for and I can feel the lever slowly open on the Motorised Honeywell valve so I know thats ok. However the boiler rarely comes on.

So the next day I tried it with the CH coming on at the same time as the HW and it worked fine - we had hot water as normal. Am I right in assuming the microswitch in the zone valve is knackered?

When the HW is called for only the lever opens and I hear a click at the boiler then nothing. But if I then turn the CH on the boiler fires straight away and we get CH and HW. If I then turn the CH off after 10 seconds or so the boiler will continue to run the HW until it cuts out to cool down as nomal. Sometimes it will fire up again after it has cooled - sometimes not. Almost like I have to call for CH to kick start the boiler for HW?

I think its either a fault tank stat or zone valve switch but thought I'd ask your opinions before I do anything.

If it is the microswitch how do I fix it? Do I have to replace the whole valve, just the head part or can I just replace the switch (my preferred option!! )

Thanks

 

[namsag]

You maybe looking too deep to start with. Basic gravity system check ball valve on header tank is not stuck and header tank has emptied.

 

[mk2phil]

If the header tank was empty then wouldn't the CH stop working too?

I assume you mean that the boiler wouldn't fire if there was no wtaer in the system?

 

[ChrisR]

Boiler would fire but gravity loop wouldn't work.
Boiler should be getting very hot on HW only - does it?
If you're getting a click at the boiler the hw microswitch is working, and the boiler can't tell where the signal is coming from so it should go. So your evidence doesn't quite make sense!

 

[mk2phil]

The boiler isn't even coming on, only when you call for CH at the same time.

I thought that the water thats pumped round the rads is the same as that used to heat the HW tank - i.e. there aren't 2 seperate curcuits, 1 for HW gravity loop and 1 for the radiator curcuit - its all one big curcuit?

Are you saying that there a 2 seperate curcuits and the HW curcuit is low on water hence the boiler isn't firing even though I hear it 'click' when the zone valve opens?