Grant oil boiler hunting

[George J]

Sorry guys, busy day today. Will be back on it in morning.

 

[George J]

With cyl stat calling for heat and CH on it runs normally. Add HW and hunting starts within a couple of seconds. My purge is closer to 10 secs.

To begin the test I turned the cyl stat right down and MPV clicked. Then turned it back up to do as you suggest. The lever moves with light touch to mid position then with some force I can open valve for CH and feel rad flow pipe temp rise.

I have multi meter but not that skilled with it. Happy on continuity and DC but AC ???

 

[Johntheo5]

What i would like is HW only on, ensure boiler firimg normally then move the lever to mid position and latch it in, there should be a fairly stiff resistance to movement, check boiler still running normally, post back.

 

[George J]

Just turned cyl stat up and HW running normally. Moved MPV to mid position until sone resistance felt. Boiler running normally

 

[Johntheo5]

Ok, as I expected.
Now turn both HW&CH on, boiler should start hunting, listen very carefully for any noise from the MPV, I'd be 99% sure that its the actuator on this thats causing the problem.

 

[George J]

what noise am i listening for - click, motor hum ???

 

[George J]

no click and no motor whirring.

Can I manually set lever to required position but I guess that won't help identify a problem to do with actuator.

 

[Johntheo5]

I thought you might hear the motor huntimg, overshooting the mid position and then reteturning to the mid position, that manual lever is only for settiing the valve to mid position while draining or refilling the system, with mid position, HW&CH on then the lever will have no resistance/effect. If you look down on the MPV casing top you should see a raised dimple on the end propably opposite end to the cable entry? If so, that actuator can be changed without removing the valve body.
Can you post a photo of the boiler labelled details, can then download elec schematic to take a few tests.
Also a photo of the MPV details.

Going back to the hunting, are you absolutely sure that the burner is NOT cutting off and on every few seconds. If it is, you should hear a "whoof" each time it fires, normally after a 10/12 sec urge.

 

[George J]

had already done MPV

was hoping that would be the case with removing actuator.

 

[George J]

I have install manual with wiring diagrams but the quality of my pics, on here, are not very clear. Heres one to test if clear enough

 

[Johntheo5]

When you say "had already done MPV", what do this mean?

To carry out test, set your M.meter to 500V (AC) the V has a squiggle after it, like mine, below, on the boiler wiring terminals, put one probe on terminal1 L and the other probe to N, do this test with both HW & CH selected and boiler hunting, whether this voltage is changing or not, do the same tests between ter 4 & N and ter 7 &N., 10 secs or so should be enough.

 

[George J]

Sorry, not clear, already done photo.

 

[George J]

I left meter on for over 10 secs for each of the 3 tests

2(N) - 1 240v constant
2(N) - 4 all over the place. Probably about 58. is most consistent reading
2(N) - 7 240 through cycles. Shows OL for split sec when switching back on

 

[Johntheo5]

Ok, thanks, repeat that test with HW Only on and post back, then repeat it again with CH only on and post back.

 

[George J]

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.