Boiler Not Firing For Central Heating, Hot Water Okay

[th71]

Hi

- Ideal Classic NF Boiler
- Drayton MA1 Mid Position 3 Port Actuator/Valve
- Wilo Pump
- acl Drayton Room Thermostat
- LP241 acl Drayton Hot Water and Central Heating wall timer/control

The boiler clicks and fires up no problem and the pump runs when the hot water is switched on and gives hot water, but if just the Central Heating is selected, there is nothing at all from the boiler and the pump does not run.

The only way to get the radiators hot is if both the HW and CH is on, the lever on the mid position valve goes all the way to the right to CH and heats the radiators

The 3 port Valve and pump are next to the cylinder in the upstairs airing cupboard.

Bled all radiators, lever on 3 port valve seems to move okay manually.

Any ideas why the boiler will not fire when Central Heating is selected

Thanks

 

[Armo74]

Sounds like a faulty microswitch
A new actuator should sort it

 

[th71]

Thanks for replying Armo74

Wondered if it was the microswitch , but wasn't sure due to the complete silence when the CH is selected

Is it possible to put a different valve on instead of the Drayton MA1 Mid Position 3 Port Actuator/Valve? I was thinking of a Honeywell as I've read they're more reliable. Or does it need to be the same?

Its a 22mm Valve

Cheers

 

[MANDATE]

I can think of three reasons why you can't get CH on its own.

To take the valve from mid position to CH there needs to be power on the grey wire of the valve. without that it wont move from mid position.

There are two micro switches in the valve head each with two sets of contacts ie 4 sets altogether. The power from the grey goes through 1 set to drive the motor. If these contacts are dirty/burnt they stop the power getting to motor.

The motor may well move over both the first and second half of the full range and reach the CH position. During the second half power is allowed out from the valves 'orange' wire to light the boiler, this is achieved by triggering the second micro switch, but again if the contacts are dirty/burnt it prevents it from operating as it should

With the boiler operating in mid position, it confirms the room stat is working and the motor is not the problem

 

[Armo74]

As I said a new actuator should sort the problem.
I personally would change the whole valve for a Honeywell one but it depends on how much you are willing to spend and how much work you feel you could do yourself.

 

[th71]

Thanks Mandate for the clear explanation. One thing I have noticed, and that is the water is scalding hot even though the cylinder thermostat is at 60, and if it makes any difference, the boiler is at 4 (out of 6)

I have noticed a Honeywell v4073a on eBay for around £35. Would this be an ideal replacement?

Cheers again