Oil boiler only runs for 15 mins at a time

[sharpener]

Kidd Very High Efficiency 60,000 BTU boiler mfd 1995, working fine until this morning. Has Inter model 2011 burner with Danfoss control box. Regularly serviced, last time in 2022, routine parts only (nozzle, gasket).

 

Starts and fires up without hesitation but stops after approx 15mins and goes to lock out. Will re-start immediately when I push the reset button.

 

Usual service engineer (ex Kidd) suggests fuel starvation. Tank 1/3 full. No recent oil deliveries to cloud the issue. Have checked the filter at the tank, no debris, changed it anyway. Disconnected flexible pipe at boiler union to copper, steady stream of oil comes out. Fire valve not tripped. AGA teed off the same pipe in house runs good and hot and even survived the filter change. No obvious point for air to be getting in to the oil feed.

 

Motor, pump, control box etc must be OK or it would not run at all. What do I try next? Am loath to spend much money as I hope to get ASHP installed next month!

[ProDave]

Pull the burner sensor out, usually optical, check for soot on the end obscuring it thinking the burner has stopped burning.

[dpmiller]

^ photocells, control boxes, and oil solenoid valves all have a terrible habit of failing intermittently. A clean photocell is a good start, but I'd expect that to cause a near-immediate lockout. Beyond that...

 

can you view the flame any way when it's running? IE does it go out then trip

Does the sound change in the seconds before it trips out? Motor slowing down, squealing or a click

Does it go *straight* to lockout or does it retry once first?

Have you confirmed the supply voltage isn't dipping because of an external issue?

 

If it doesn't attempt a re-start at all I'm going to suggest controlbox. Pop it open if you're brave and have a look for dodgy capacitors and dry joints, give any accessible relay contacts a wee clean

[Conor]

Is there a bypass between the flow and return loops? Sounds same as the issue we had on a gas boiler, bypass valves had failed in open position, meaning hot water was returning directly to the boiler and causing it to lockout after a few minutes. 

[dpmiller]

And... (now that I think about it)

 

Get the literature for that exact controlbox- they come in many configurations- There might well be a list of faults that take it straight to lockout, and there may be a way of getting blink codes out of it too

[sharpener]

3 hours ago, dpmiller said:

^ photocells, control boxes, and oil solenoid valves all have a terrible habit of failing intermittently. A clean photocell is a good start, but I'd expect that to cause a near-immediate lockout. Beyond that...

 

can you view the flame any way when it's running? IE does it go out then trip

Does the sound change in the seconds before it trips out? Motor slowing down, squealing or a click

Does it go *straight* to lockout or does it retry once first?

Have you confirmed the supply voltage isn't dipping because of an external issue?

 

If it doesn't attempt a re-start at all I'm going to suggest controlbox. Pop it open if you're brave and have a look for dodgy capacitors and dry joints, give any accessible relay contacts a wee clean

 

Can't view flame but I can hear the burner stop firing a few seconds before it locks out so my suspicions are on the solenoid. Startup and shut-down timings are OK so I don't suspect photocell or control box. Don't think it is meant to try re-lighting on flame failure outside of the startup sequence.

 

No problems with voltage dips and there is no hydraulic bypass. Will see if there is an old pump in the garage.

[sharpener]

1 hour ago, sharpener said:

 

Will see if there is an old pump in the garage.

 

There was, fortunately, and the solenoid from it seems to have fixed the problem. Boiler has been cycling on and off on its thermostat ever since. Beats me how a coil of wire on a former can be quite so unreliable, it's not exactly new technology. Might cut the old one open when I have a spare moment.

 

16 hours ago, sharpener said:

Am loath to spend much money as I hope to get ASHP installed next month!

 

Two of the four installer people who came for a further site visit this morning are expecting additions to their families, so now it has been put back until April. Funny this was not known about when the dates were put in the diary in December.

 

 

Edited February 13 by sharpener

[dpmiller]

Those Danfoss coils are quite unreliable. They're quite small for a mains coil...

 

They were hard to get for a while  and I found that the coil out of a washing machine inlet valve was a physical fit

[sharpener]

On 13/02/2024 at 15:36, dpmiller said:

Those Danfoss coils are quite unreliable.

 

Yes so it would seem from comments on various websites. Disappointing for a major brand name. And expensive for what they are, the cheapest I found from a reputable-looking source was £27-99 IIRC.

 

On 13/02/2024 at 15:36, dpmiller said:

They're quite small for a mains coil...

 

I recently wired in a miniature 240V mains relay which has an even smaller coil. And over the years I have had quite a few dealings with specialist coil winders over microphone transformers, mains toroids, voice-coil type actuators. Don't recall any problems with them going open-circuit intermittently or in response to thermal stress.

 

But funnily enough I was going to put in a plug for St Ives Windings and then I found this so may be it is not that uncommon. Must dig some old Neve mic transformers out of my junk box, no idea they might be worth £150 apiece. But I digress.

 

Edited February 14 by sharpener