Mid Position Valve Issues

[eddr]

Hi All,

I'm hoping some of you knowledgeable people can help me with this, I have searched the forum on similar issues with 3 way/mid position valves but none have really answered my questions...

Basically the past few days, I have noticed the heating hasn't been coming on when it should - it's being called but the 3 way valve (Which is a British Gas MV22M) doesn't want to move to the right position.

I have managed to figure out the following (Some which may be normal functionality);

- When there's no call for HW + CH the valve stays in which ever position it was last in
- If the valve is on CH only and then CH is turned off, it returns to HW only when the stat is turned up
- If the valve is on HW only and CH is called for, it doesn't move!
- If valve is moved manually to the middle and CH is called for (HW off/stat turned down), it does not move to the left position
- If valve is moved manually to CH only position, when HW + CH is called for it does move to the middle.

So it's almost as if the valve if on HW doesn't move to CH+HW or CH only. It seems to move from CH only to CH/HW ok...

I'm quite confused by this, no wiring has been touched & I have made sure everything is connected as should be.

I've attached a picture of the valve - does it look like this is a replaceable one? Would changing the motor be beneficial rather than a whole new valve ? (Obviously a lot cheaper and less effort).

I'm not 100% convinced it's the valve, but moving it manually does fire up boiler & pump as and when it should in all positions.

Thanks in advance for your help!

Untitled

• eddr
• 27 Mar 2013
• 1

 

[Armo74]

If the boiler is firing when the valve is manually moved then the synchron motor needs replacing.

 

[eddr]

Ok can I replace this myself? Looks like a easy job...

 

[eddr]

I have replaced the motor but sadly has made no difference

A few times I have been able to get it to move from CH+HW to CH but its not consistent.

 

[seco services]

Sounds more like a micro switch or board fault.

 

[MANDATE]

The (first) micro switch has two sets of contacts like a two switch.
One set takes power from room stat to drive motor to mid position.
This power is then lost when the micro switch is triggered, but power is available (or should be) on a different wire (grey) to drive the motor over the remaining half. It does this using the second set of contacts. If these contacts are dirty/burnt then motor will not go beyond mid position.
There are also times when the motor moves as it should but the boiler fails to light. This is due to dirty/burnt contacts on the second micro switch which allows power out from the valve (orange)
If it did work ok previously then replacing the valve head is the best, but its also worth verifying the wiring is correct. Especially the wires from programmer HW OFF terminal and cylinder stat, both of which go to the 'grey' of the valve. It's these that supplies the power for the last half of movement and if that is not there, the motor does not continue.

 

[eddr]

Thanks for all your replies so far people, very much appreciated!

I think I'm going to try and nail it down using a multimeter, hopefully this will give me a good indication where the problem is.

So basically from what has been said, it's either the micro switch(s), board fault/actuator or the actual valve?

I will most likely replace with http://www.heatingcontrolsonline.co...a16793-midposition-motorised-valve-p-110.html