CH problem - thermostat, programmer or motorised valve?

[dibely]

Hi,

Our central heating has stopped working recently (it was OK last week although it was probably the first CH use for some time) and I am trying to find the cause.

When I switch the central heating on at the programmer it doesn't trigger the boiler to fire up at all or for any water to pump through the radiators but the light does come on to say it's on, just nothing happens. The hot water on the other hand is working fine firing up the boiler etc.

I checked the FAQ's and found an article about getting water around the radiators by setting a lever on the 3-way motorised valve to a mid position which works so I have a temporary solution but does this mean the valve/motor is faulty or is it more likely to be the programmer or thermostat that is preventing the boiler from firing in the first place?

Judging from the varous similar posts on diynot I am leaning towards the valve being the cause but I didn't want to rule out the other two without checking as I am not sure what the sequence of events are between the thermostat/programmer/MV.

Any help greatly appreciated,

Dibely

Additional info:
Open vented system
Ideal Classic NF type boiler (1992)
Honeywell programmer (mechanical)
Honeywell thermostat

 

[seco services]

if its working when the lever moved across its pointing to a motor faulty in the actuator.
remove the actuator cover and test for power to the motor when calling for heat.

 

[namsag]

3 port valve 90% of time it will just need a new motor other 10% it will be the board in the valve gone and a new head or complete valve wil be req.

 

[dibely]

Thanks for the quick replies!!

OK I will go dig out a multimeter to test the motor.

 

[dibely]

After testing the wires in the valve I get the following:

CH only on at programmer:
240V on the white wire
0V on the orange wire
Can't test the grey one as it is too difficult to get to

I think from this the request for heat is coming through to the valve but the motor doesn't start so I guess I need to replace this.

However one thing I noticed, that I forgot to mention previously, was that if I move the lever up to it's topmost position, which I assume would be the same as if the motor had moved it to the CH only position, the boiler still doesn't fire. Shouldn't the boiler fire if I do this with the CH on at the programmer??

So far the only way I have got the CH to circulate is with the HW on at the programmer instead and the lever at the midopoint.

I'm not sure if this means there is something more than just the motor that is causing the problem but then again I am not totally versed with the inner workings of the motorised valve.

Can I get away with simply replacing the motor or do I need to replace the entire valve?

Thanks in advance,

Dibely

 

[MANDATE]

I'll try to describe it briefly! This is for CH only! Programmer feeds the room stat, the room stat feeds the white wire of valve. valve moves to mid position. Microswitch is triggered (switches to grey wire) grey wire now moves valve to CH only position. whilst doing so it triggers second microswitch and diverts power out through the orange wire to light boiler.
The lighting of the boiler when HW is involved in the demand comes direct from the cylinder stat.
I've experienced two similar problems. One was due to a faulty microswitch (motor ok) and the other due faulty motor (microswitch ok)
I understand the lever does not move the valve fully across to the CH only position. Its purpose is to latch it at mid position for filling the system. I believe it may go a little beyond mid point and that is where the second microswitch is located.
The other problem is the freeness of the valve spindle, if it is stiff then the motor cant cope.
Best thing is to remove the actuator off the spindle and test.Also test spindle for stiffness. A replacement motor costs around £16 and a replacement actuator head over £40.
hope it helps.

 

[dibely]

Just wanted to say thanks for the replies - it was the motor after testing which was duly replaced and now we have central heating again!!! The wife is now very happy!

Many thanks again for the responses!

Dibely