Grant oil boiler hunting

[Johntheo5]

I think it just means that ter 7 is just linked to ter 1, the switched live, and yes 2 to 10 if they read 240v are fine.

The MPV should certainly move right over to CH only (port A open) when CH only is selected and not apparently be in the mid position feeding both CH and HW., this could be a programmer fault (as suggested above) because the HW OFF contacts actually power the valve to the CH position. The other strange reading is the HW only test which you might do again some time, shows this N to 7 voltages of 6V to 180V yet N to 1 is perfect, also the boiler runs perfectly.
What you might do, CH & HW both on but turn the cylinder stat right down and see if the valve now moves to the CH position only, with no HW cylinder heating, this would point to the HW OFF contacts faulty or maybe never connected?, however any of this still shouldn't IMO cause the boiler to hunt since all reading of N to 1 (the switched live at the boiler) show a steady 240V so don't know where the answer is, lets see what you get with this test above.

HW only
2(N) - 1 240v constant
2(N) - 4 all over the place
2(N) - 7 random figures as low as 6v and up to 180v
I don't have a room stat just TRV on rads.

 

[George J]

Thinking I might try replacing either the actuator on MPV or programmer. Of the 2 options I fancy replacing the Programmer first. If problems continue I could replace actuator.

Is this the wisest way to go.

 

[Johntheo5]

Yes, probably the way to go, programmer first, above test might show something but you have to start somewhere.

 

[George J]

I tried the cyl stat right down with CH running and still have cyl being heated.

Seems folk are associating the hunting problem as common with the programmer.

As a layman am I right in thinking that as boiler 'can' operate normally, must the problem be with the programmer or MPV.

 

[Johntheo5]

I assume you had HW selected at the programmer?? with cyl stat turned down, if so, then this would point more to a MPV fault IMO.

I would have never associated my understanding of boiler hunting with a programmer/MPV fault, if the boiler was doing a 10/12 sec purge every time then yes, the "hunting" I have ever heard was on my own boiler in 19 years and sounded like the burner lighting on and off every few seconds (no purge) which I believe was/is something to do with the flame becoming detached from the burner momentarily or something like that but since your hunting problem is only happening in valve mid position then its only logical to assume it must not be a boiler problem.

 

[George J]

The nature of the fault with the programmer in the above video is very similar to mine. I found a second video that is encouraging me to buy a new programmer rather than replacing capacitors etc. in the existing.

I think a new programmer is a good place to start as if that is not the problem then I will have a spare in stock ???

 

[spannerzone]

The nature of the fault with the programmer in the above video is very similar to mine. I found a second video that is encouraging me to buy a new programmer rather than replacing capacitors etc. in the existing.

I think a new programmer is a good place to start as if that is not the problem then I will have a spare in stock ???

I would absolutely consider the Honeywell controller as a likely contender for the fault and it's a relatively simple thing to swap out (two screws and lift it out). I think my boiler went on/off/on/off every few seconds when trying to run CH and it was the relay in the controller opening/closing every seconds as the power to the relay kept failing. With mine I turned off the LCD backlight as per the video I listed and it immedietly restored service so was very clear as to where the fault was. My controller was from 2010 and I think there is a batch around this time that might be affected but could potentially affect any dated controler as quite frankly, they're a terribly cost reduced design for something that needs to run 24/7/365

I did get replacement capacitors and fixed mine but I had already replaced it for a new controller.... I repaired the old one to have as a spare and I'm an electronics engineer so can't just thrown things away. However my controller cost £70 so hardly a big deal to replace every 10 years or so.

 

[George J]

I'm a locksmith so swapping capacitors is not an everyday task. Will pick up programmer on Monday. If the problem remains I will swap back to old one and keep the new one for when its needed. I will share the results on here. Fingers crossed.

 

[Johntheo5]

When you are changing the programmer, also ensure all the boiler block terminal screws are tight.

 

[George J]

Just replaced programmer and, fingers crossed, all going well. Had CH and HW on for 15 minutes and just turned off CH and waiting to see if MPV is working correctly.

Will check screws. Good reminder. Thanks

Thanks to you all.

 

[Johntheo5]

Also, sometime, check that the valve is going fully over to the CH side, (port A open only) by doing two tests, (1), with CH & HW calling just switch off the HW and ensure the valve moves across, and (2), with CH & HW calling turn down the cylinder stat and check that it again moves fully across.