Worcester Heatslave burner motor won't start when warm

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Hi, I hope somebody can point me in the right direction with this.

I have a Worcester Heatslave 20/25 Oil-fired combi boiler (c.1999) with an Inter 2011 burner (Bentone 90w motor + Danfoss BFP11 3L oil pump, two pipe system) and room sealed balanced flue.

Boiler normally starts ok from cold and will run for between 30min to an hour before burner switches off without water reaching thermostat setting. Turning fascia thermostat down and then up to restart burner results in a bit of twitching and attempted turning of the burner motor (a bit like a dodgy starter motor on a car). Sometimes the burner will restart like this, especially if allowed to cool for 30mins but usually not.
I have checked that the fan impeller is clear, cleaned the flue, the photocell and all oil filters, renewed the nozzle and oil lines, and checked that the electrical plugs are pushed home. I have even tried swapping out the motor with a known working one.

All the water pumping side of the boiler seems fine and the fascia thermostats, DHW, and CH work ok when the burner's actually going. The burner problem doesn't generate a lock-out, it just clicks off and won't restart without a good rest and a lot of twitching and sticking.

I'd really appreciate any suggestions that might help me narrow this down.
Thanks.
 
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If you swapped the capacitor with the motor, its either your oil pump, or the motor capacitor. I'd suspect the capacitor.
 
Hi Oilman, and thanks for coming back so quickly.
The new motor was supplied (on sale or return from my local store) with a new capacitor attached so is presumably working ok.
Is it possible that there is an intermittent fault on the oil pump? (since the burner runs for up to an hour at a time), and if so is it possible to check the functioning of the pump before forking out for a new one?
 
yep i would say pump is jammin . was the drive dog ok....i mean a nice tight fit. cos they do wear and spin a bit on shaft. ooerr.
 
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There's some problem going about where the seals seem to be binding on the pump shaft when they get hot. You could take the pump off when its cold and try turning the spindle, then do the same when it's hot. If you have a sterling burner, you could find the fan and try turning that.

The cure is a new pump if that is the problem, unless you fancy changing seals.
 
Hi Wilhelm and Oilman,
Thanks for the ideas; the drive dog is ok (he sends his regards), the pump seals sound like they could do with a closer look though. The spindle turns freely enough when cold, I'll go and warm things up now and see how it turns then.
Thanks again guys.
 
If as the OP says the burner never generates lock-out and starts after "30 min rest" wouldn't it be better to check for voltage at the burner before swapping parts. Bentone burners (unlike Riello) will lock-out on just about all (except combined transformer/control box) faults.
 
You could be right, but checking the pump stiffness is something that can be done whitout changing the pump, and it might rule it out. It does sound a bit more mechanical than electrical with those times, and itwould be easier to see when you're there. There may be more than one fault, like stiff pump AND dicky control box.
 
yes nixt, i didnt read that bit, it should have locked out.

can i change my mind.......to control box. i think ive seen those old bho 's on a 2011. the tan coloured ones. id wire in a satronic or put a 930 base on it. etc etc..
 
Remember its a combi Oilman and I'm sure you know all that might mean.

'Runs for 1/2 hr and shuts before water hot'.

Worth checking circulating pump, motorised diverter, and even if primary side of plate dhw ex is not blocked. If it fires for 30 mins its usually enough to satisfy heat bank.
Also if boiler fires when 'Sika' paddle flow switch is operated by tap. Then if power to burner and it does not light begin burner fault finding.
 
Nixt said:
Remember its a combi Oilman and I'm sure you know all that might mean.

Yes. Get someone in,


.......like wot companies do to me as they don't work on the water bits.
 
Latest update....
I decided to start by following Oilman's advice and check the turning of the oil pump spindle when cold and warm to see if its binding.
I started to boiler and waited for the burner to stop and refuse to start again but....it ran perfectly for about 5 hours until I gave up waiting for it to fail and went to bed.
The only difference that I can think of at the moment is that on this occasion I had both the CH and DHW on at the same time. Previously the DHW had been switched off once the DHW tank was full of hot water.
To test this theory I've switched both on again this morning and so far, so good. On the assumption that this continues I shall try later to see if my original problem returns when trying to run just the CH without DHW switched on.
If I do need both DHW and CH switched on together in order to allow the burner to restart does anybody have any clue why this would be?
 
Burner power connector not pushed in.Diverter valve. Thermostat. Circuit board.
 
Just cause the burner isn't firing doesn't mean its faulty. Nothing you've put down so far indicates a burner fault. But being as you prefer to carry on aimlessly, I'll leave you to it.
 
Nixt said:
Just cause the burner isn't firing doesn't mean its faulty.

Fair point, hence my last post.

But being as you prefer to carry on aimlessly,

That was yesterday, but I'm sure you did some trial and error approaches when you were learning.

I'll leave you to it.

Or give some advice?
 

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