3 Port Valve problem?

[crxdave]

I've got an issue that has recently developed in my HW/CH system..

In order to get my boiler to turn on for the hot water, on the controller I must switch the HW to on, then switch the CH heating on & then off. Once I do this the boiler will fire. Could this be the 3 port valve sticking?

 

[D_Hailsham]

I've got an issue that has recently developed in my HW/CH system..

In order to get my boiler to turn on for the hot water, on the controller I must switch the HW to on, then switch the CH heating on & then off. Once I do this the boiler will fire. Could this be the 3 port valve sticking?

Possibly, although the valve plays no part when it is HW only.

To check if the valve is sticking:

Turn power off (not just HW and CH off at programmer) to reset the valve.
Move the lever at end of valve from Auto to Man
You should feel resistance.
Lever should return to Auto when released.

If OK, valve not sticking.
If no resistance or lever does not return, valve sticking.

Sticking valves can sometimes be rectified by using silicon lubricant. Remove the actuator (box part) to get access to the spindle.

 

[Boilerman2]

Is your programmer a Honeywell ST9400?? if so it is probably faulty (this is a known fault)

 

[crxdave]

Nope - it's a Drayton LP522.

Also, I forgot to mention that the problem also occurs when trying to switch the central heating on. So the pattern is: switch CH to on, then switch HW to on, then off - boiler then fires...

 

[D_Hailsham]

Have you checked if the valve is sticking?

 

[crxdave]

Possibly, although the valve plays no part when it is HW only.

To check if the valve is sticking:

Turn power off (not just HW and CH off at programmer) to reset the valve.
Move the lever at end of valve from Auto to Man
You should feel resistance.
Lever should return to Auto when released.

If OK, valve not sticking.
If no resistance or lever does not return, valve sticking.

Sticking valves can sometimes be rectified by using silicon lubricant. Remove the actuator (box part) to get access to the spindle.

Tried this last night, and exactly as you said, the lever returned to auto...

I guess this points to a problem with the programmer?

 

[D_Hailsham]

Tried this last night, and exactly as you said, the lever returned to auto...

I guess this points to a problem with the programmer?

Possibly.

Presumably the programmer is currently set to 'timed' HW, i.e 2 or 3 on periods a day. Set the CH to OFF and the HW to ON, i.e permanently on. Does the water now heat up? (Turn the cylinder stat up/down to check) If it does, the programmer is faulty. If it doesn't, the cylinder stat needs checking as well as the voltages. This is all explained in Mid-position valve operation and fault finding.