Potterton Promax SL 2 years old :( wont shut off

[bolst3r]

Noticed the rads were boiling last night when they should have been off fiddled with the stat last night and nothing happened so looked at it in more details this morning and found the following:

When I turn the Honeywell room stat down, the flame symbol on the stats disappears and I hear a click I wait a few minutes at the boiler but I can still see the burner through the viewing hole burning bright.

Next I turn the HW and CH to off on the programmer, wait a few minutes at the boiler but I can still see the burner burning through the viewing hole.

Next I turn off the electric to the boiler, and programmer and everything shuts off. I give it a couple of minutes and turn the power back on. The boiler remains off

Next I turn the programmer to cont for both HW and CH and still the boiler remains off

Next I go to the room stat and turn this up until the flame symbol appears and I hear it click. I then watch the boiler and 20-30 seconds later it fires up

Next I go back to the room stat and repeat the first step but the boiler remains on

Guess at this stage i'm trying to narrow it down to either a boiler, room stat, or MV issue but not sure what process to check/follow next

Thanks for any help

 

[45yearsagasman]

Chances are that it is a motorised valve causing your system to remain on, either a sticking end switch in the powerhead , or the valve is siezed and not returning to the fully closed position.
Which type do you have? View media item 30391 View media item 38425

 

[bolst3r]

Hi thanks for the quick response and the images, they are the same as the one on the left with the red arrow on it. There looks like a 22mm and a 28mm one. Was going to get the initial installer out to look at it but couldn't get hold of him and just heard he is on holiday.

Is there anyway to test the valves or a manual override? I can see the trigger that's sticking out... Looking online it looks like I can replace the top/motor or the complete, just need to workout which one is faulty (if this is the problem) and be able to ascertain if it's just the switch/motor that needs replacing or the entire unit...

 

[45yearsagasman]

Then the most common cause is that the end switch on one of the valves is remaining closed either by sticking or the valve is seizing.
Identifying which one is the 1st stage and for that you will need access to the wiring centre and the use of a multimeter or similar voltage tester.
If you are not confident then a good repairman will ID this in 5 minutes and depending on the fault (switch or seized valve) will be able to effect a repair.
If the silver cover has a raised dimple, then the head is replaceable on it's own.
The orange wire from either valve should be 0 volts when the valve is closed.

 

[bolst3r]

My Dad is a sparks and is due round tomorrow but CH isn't his bag. I've turned everything off as I don't want the boiler running all day and just out of interest tired moving the handles on the valves slightly to see if they move. The trigger on the 28mm MV moves like a hot knife through butter but the 22mm MV trigger moves like it's rusty inside and feels like corroded metal rubbing against metal. I assume this should move freely like the other MV?

 

[45yearsagasman]

The only way of finding the fault is removal of the covers and checking the operation as previously described.
With respect a CH repairman is a better bet than a sparks who admits that CH is not his forte.

 

[bolst3r]

Yes, I think you are right. However i've looked at the labels on both valves and they both say for replacement heads use part 40003916-001 so I think I will get one replacement then get my Dad to try it on each valve, that way if one is faulty then it should fix it and only an hour is spent trying to fix it. If this fails then it's either both valves, which would be very unlucky or the actual valve is broken but I hear this is quite rare... I will also then be left with a spare MV head for when one eventually goes. It's funny as soon as I told my Dad is was Honeywell he said that explains it, he said he would replace it for a Danfoss or something more reliable...

 

[45yearsagasman]

Ask any heating engineer, and Honeywell would be first choice. Don't know who your Dad got his info from. Using another make involves changing the WHOLE valve as parts are not compatible. Leave it to you.

 

[bolst3r]

Yup, sounds like you are right, was about to go for an exact replacement but the symptoms have subsequently changed which makes me think it might not be a MV.

Basically I set the programmer to off for both CH and HW and the boiler continues to burn however it seems to be at a lower rate and after 20-30 minutes I find the boiler has finally stopped and no flame is visible. 10 minutes later I go back to the boiler is burning at the lower rate flame even though the programmer is set to off for both CH and HW.

Very strange...

 

[bolst3r]

So ran some other checks and after playing with the override trigger on the MV it started behaving properly which made me think it was a sticky motor. I then removed the top part of the valve and was able to turn the spindle by hand which clarified what I thought so after a quick purchase and replacement it's working correctly again. Don't know it the spindle is a little tight and caused the motor to burn out of if it just wore out, either way i've located where the fault lies so if it goes again i'll replace the whole assembly. Thanks for you help, invaluable gain