Central heating only works with Hot Water ON

[AllenDee]

Hi,
I have a gravity fed system with 2 separate valves for hot water and central heating. Here's what's happening, and I'm really scratching my head here:
The only way to make the central heating work:
- Switch off the central heating from the controller.
- Bypass the central heating valve and lock it in
- Switch on the heating
- Pump starts
- boiler works, hot water + all radiators heat up - until the hotwater tank reaches it's max temperature.
If you don't switch off the central heating from the controller, then after few minutes the mororised valve unlocks the valve, returns to close and switches the boiler off.


If you use it as normal, and switch ON the central heating, the central heating valve motor opens the valve, boiler starts up, after 5 minutes or so, the boiler turns off, and the pump stops.
I just changed the circuit board with a new one - same thing.

HELP Please !!

 

[Stuckinarut]

I'm not sure why you changed the circuit board as do a lot of other posters. The issue is the motorised valve by the sounds of it, it's not sending a switch live correctly to fire the boiler.

 

[Madrab]

Central Heating only works when Hot Water is ON

Hi, I have a gravity fed system with 2 separate valves for hot water and central heating. Here's what's happening, and I'm really scratching my head here: The only way to make the central heating work: - Switch off the central heating from the controller. - Bypass the central heating valve and...

www.diynot.com

Duplicate

 

[AllenDee]

Thank you for your reply and taking the time.
The motorised valve for the central heating does indeed come on, and fires up the boiler - only that after few minutes boiler shuts down and the valve goes to closed position again, and after another 5 minutes, comes ON for another 5 minutes.... Only way to get the central heating going, is to switch off the central heating from the controller (hence switching off the motorised valve) - and bypass the valve manually, and switch ON the hot water. The boiler is a Potterton 80F.

 

[Stuckinarut]

So is the room thermostat satisfied (at temperature) then?

 

[AllenDee]

room thermostat OK, also did a test with a multimeter. At the point when boiler switches off, the thermostat is still in closed position.
Boiler thermostat(s) OK too as no issues heating the hot water tank all day long. Sludge in central heating pipework? but then why are all the radiators burning hot when I bypass it all...

 

[Johntheo5]

Are you saying that you are getting 230V continuously between the brown wire from the roonmstat to the mororized valve and the neutral from the motorized valve even when/with the motorized valve closing/closed.

 

[AllenDee]

 

[AllenDee]

When the boiler kicks in (central heating only) - I can switch it off/on with the room thermostat.
That is a VERY helpful diagram though.

Might take a punt, replace the motorised valve (only the motor). If the micro switch is playing up, that would be it.
What do you reckon?

 

[gas112]

change valve motor

 

[Johntheo5]

When the boiler kicks in (central heating only) - I can switch it off/on with the room thermostat.
That is a VERY helpful diagram though.

Might take a punt, replace the motorised valve (only the motor). If the micro switch is playing up, that would be it.
What do you reckon?

This seems to be saying..... anf if so, its not the micreoswitch (end switch) that is is playing up but could be the motor, so, as suggested either replace the motor or the actuator?
"The motorised valve for the central heating does indeed come on, and fires up the boiler - only that after few minutes boiler shuts down and the valve goes to closed position again, and after another 5 minutes, comes ON for another 5 minutes"

 

[AllenDee]

Got a DRAYTON motor from Screwfix. Slot it in. Half hour in, and still purring away!!! Actuator was OK it seems !
Boom! Thanks troop.
That diagram John is GOLD!

 

[Johntheo5]

Well done.