Worcester Heatslave 15/19 runs then locks out

7 Mar 2016
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United Kingdom
Boiler locked out over the weekend. Oil was very low, in fact I assumed we'd run out; although in hindsight I don't think it was that low. Got a full tank today but the boiler runs for about 5-10 minutes, enough to give us a storage tank of reasonably warm water, and then locks out the burner.

Often, waiting 15-20 mins lets the boiler fire and run again for several minutes, but not always.

I've bled the oil pump. Cleaned out the filters by the tank and in the oil pump. Cleaned the photocell, although it looked clean. Checked the pump solenoid coil, which seemed fine but I've swapped it for a new one I had anyway.

I've had the nozzle out, soaked in kerosene and given it a rub with a toothbrush. I'll change that soon anyway, but doesn't fit with the 5 minutes of running and then nothing for a while, does it?

Is there anything else I can be checking?

Thanks for any advice.
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The solenoid coil is the obvious one here.....are you happy it's good?
Stand by the burner if you can next time it gets huffy - just to determine that the motor is actually spinning, rather than just trying to. (Possible motor start capacitor failure).
Don't try to clean the nozzle, use a new one.
John :)
Thanks John. I will get a new nozzle. New coil was fresh from the sealed packet, but the old and the new can be felt exerting magnetic forces on a screwdriver when detached from the solenoid. It all sounds normal. Fan starts, can hear the ignition and the burner kick in. Runs for a bit and then just stops.
Is it the Heatslave RS version with the sealed tin encasing the burner? Try running it with the tin cover off for a while and see if it keeps going. In the scenario you have described this will give an indication whether something is failing in a heat related way.

It is damaging to a nozzle to touch the tip,scrubbing it with a toothbrush is therefore not the best idea! The clever atomising bit happens inside. When you open the burner pressure test port, do you get a steady flow of oil out? If not, then this is probably where you should start, particularly if the burner (oil pump) noise changes slightly before it locks out.
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Sure, that's a pretty good test for the coil but heat is its worst enemy......its a good idea to check its electrical resistance when its cold, and again when its hot.
Are you happy that the burner is getting a good supply of oil? Disconnecting the flexy pipe at the pump and checking that for flow isn't a bad idea.
I'm assuming that the burner runs up to temperature then the stats close it down - and then it just won't light up again......can you confirm that?
There is a possibility of course that the flame is darting around a bit and sometimes the photocell can't see it, and I'm wondering if the oil pressure is correct and a flue gas analysis has been done at some time......have the baffles been cleaned recently?
John :)
PS: You can damge the coil by energising it when detached from the valve stem.
Thanks guys. Plenty of oil coming through, I have had the flexi hose off. And I beld the pump using the commisioning instructions; port open with the boiler running, spraying kerosene into a bowl. Repeat 3 times.

It is an RS model. Have been running it with the cover off just because I have needed to reset the burner so many times. What difference should that make to the running?

Once hot it does tend to then cut out a few seconds after firing up on the restart (a few seconds after firing, not a few seconds after starting the fan). But it doesn't always do that. Might get a couple of multi-minute runs out of it.

I'll test the new coil resistance tomorrow when it's cold and hot just to be sure. I fitted it cold today and the burner locked out in seconds. It has subsequently run for minutes, so I don't think that's it. But will confirm.
let us know when you have changed the nozzle. Als, when was it last serviced with a pump pressure check and flue gas analysis? Lockout 5 secs after firing is classic flame sensing but could be due to unstable flame. Running without the cover on will weaken the mixture and overairing can cause flame lifting. If the flue is leaking in the air duct, that will cause lock outs. It really needs looking at with an experienced eye.
Thanks. Will take me a couple of days to get a new nozzle. No one vaguely local has one of the same spec in stock. Will update. This morning, from overnight cold, it ran for about 20 minutes, and then stopped on the hot water thermostat. When the diverter valve changed to CH the burner fired again and locked out after 12 seconds of burning (plus 5-6 seconds fan). And has repeated the 6 second fan, 12 seconds burn, lockout, cycle for the next 3 resets.
When the boiler is off and cool, it could be worth your while inspecting the baffles / flue ways......essentially its boiler top off, which reveals a cast plate secured with two nuts.
Lifting this clear allows you to remove the baffles for cleaning, and there should be an installation diagram there too - but keep them in order anyway. You shouldn't find much free carbon but rather some yellow sulphur deposits plus some general crap to be vacuumed away.
I'll definitely confirm that any fiddling with a RS flue plays hell with the burner!
Oil pressure gauges are cheap and easy to use - alas, FGA machines are pricey. Often enough there's details concerning pressures and CO2 emissions near the baffle diagram.
John :)
Sure - on my 12 -14 boiler, nothing changes regarding the FGA with cover on or off.....at one time I did consider drilling the cover box appropriately so I could adjust the air door with the box on, sealing with a grommet afterwards but never got round to it.
My comment regarding flue fiddling refers to a home made LLD terminal guard that someone had created. Although it didn't look like it could possibly cause any issues, it certainly did!
John :)
I know what you mean, setting them up is a bit like a Grant outdoor module with the door on and off every other minute.
Ta. I'll look at that later, and I'll confirm the solenoid coil hot / cold resistance too. I did clean the baffles at the start of winter, so hopefully nothing untoward in there.

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