Boiler not starting on CH but works on HW

[cooper505]

Hi

I have an old back boiler which runs the hw and ch in my house. it has been running fine for the last 6 years being here.
I replaced the timer which was an old switchmaster (clicking thing) to a newer drayton tempus 7 a couple of years ago and all was working fine till now.
When the timer asked for hot water all is well, i can hear the boiler fire up. But when it asks for centrel heating nothing happens, boiler does not fire nor do radiators get hot.
If i turn on hw the rads stay cold. (As they should do) But if i turn on both the hw and ch then the boiler fires up and the hw and rads get hot.

Its as if the timer is not telling the boiler to fire up. Which is what i thought and replaced the timer with a new one (Same model) today. But still no joy. Does any one have any ideas?

Hopefully

Cooper

 

[gas4you]

If you have any zone valves check the ch one.

If you have gravity HW then check the pump, but from your post it sounds like you have a fully pumped system.

See FAQ's on how to check zone valves.

 

[Agile]

It sounds as if you have a motorised valve which has failed.

There are several configurations of systems which you might have!

Tony

 

[cooper505]

I have a fully pumped open system.

would this then point to the valve being stuck in the position

I dont think a have any zone valves, the only vavle i can find is a 3 point mid position, which may be my problen area then?

Thanks for the quick response....wow!

 

[gas4you]

Yes the 3 port valve head will be the problem. The microswitch will have broken that tells the ch to come on.

Set the valve to manual with the lever at one end then turn on the HW. The rads should get hot when the HW is on.

This will get you warm temporarily, but HW will be very hot so be careful when using it.

 

[cooper505]

Hi Dave

I tried that with the valve, i pushed it across to the open position with the hot water only on, but it moves back like magic!
Should i just move it across a bit and not all the way. The valve is the an old landis and gry one which from research is the same as the siemen mav322 if that means any thing to you!

 

[gas4you]

There should be a small indent that will lock the lever.

Usually if you are unlucky enough to have one of these old valves, you will need to replace the entire valve and head together.

I normally use the Honeywell or Danfoss valves.