Problem with old Thorn oil boiler

[Tom]

Our old Thorn ODY-3 oil boiler has been playing up in the recent cold weather. On a couple of the coldest mornings we have woken to a cold house and found the boiler locked out. After 2 or 3 attempts it will reset and run fine all day. I have set the programmable room stat so it has been working all night and then it is fine in the morning so it only seems to happen when it has had a long idle period and a chance to cool right down. The oil in the Tiger Loop and the filter looks clear and clean and I don't think it has been cold enough for the oil to start waxing. This is only our second winter in the house but last year it was fine even though there were some much colder nights. The only change to the boiler over the year was a new pump fitted last spring when it was also set up with a gas analyzer by the engineer. Any ideas what the problem may be?

Cheers Tom

[Nick]

Hello Tom, just what you do not need at this time! I don't know what a Tiger Loop is. (have googled and read for 20 mins, and I think I can happily live without any such gadget) My suspicion is that there may be sufficient water in fuel to (a) prevent ignition or (b) freeze and thus prevent ignition. Is the flow from your storage tank to the boiler simple or convolute? IE., are there any pipe runs where h2o may gather and/or freeze? Is it possible that your storage tank contains some water? You doubtless know that oil is lighter than water. I have used oil fired CH for about 50 years. One day I hope to learn the mysteries. Hope you are able to solve this problem quickly & satisfactorily.

Good luck & best wishes for a warmer new year,

Nick.

[Dave Liquorice]

Not sure how water in the oil would prevent ignition it won't mix so unless it is down hill *all* the way from the tank to the pump inlet the water will collect at the lowest point and stay there. The flow rate isn't enough to flush it from the lowest point.

That would be my bet. Got us last winter. Removed a slushy ice plug several inches long from the oil pipe then spent the rest of the day trying to clear all the gunk that has got dislodged and blocked the fire valve in the process of removing the ice plug...

It's not wise to try reseting an oil burner more than once without finding the reason for the lock out. If it is fuel starvation you can damage the pump.

[Michael Chare]

If you have filters with paper elements in the oild supply, these will clog over a number of years and must be changed.

If you don't change the jet, the old jet will wear and let to much oil into the boiler, this will cause soot on the photocell.

[Tom]

Thanks for the replies. The pipe from the tank does go underground for a couple of yards so there is potential for trapped water there. I have drawn a jar full from the bottom of the tank and it is clean with no water in it. There is a glass bowled filter between where the pipe resurfaces and the Tigerloop and there is no water and not much crud collected in the bottom of that.

When the boiler failed to light after lock-out the motor didn't start up, the only noise was a buzzing that went on for about ten seconds or so then stopped and the light came back on. On the third or fourth go, when the boiler lit, the buzzing lasted only a couple of seconds then the motor started and the boiler fired up.

It's working for the moment and hopefully will carry on through the cold weather forecast for the next few days. I've called an engineer but he's unlikely to make it this week so it's fingers crossed.

Tom

[Huge]

The buzzing is the ignition electrodes (much like a spark plug). The startup sequence is generally something along the lines of 10 seconds of fan running without fuel or ignition, in order to purge the burner, then fuel and electrodes (the buzzing noise), then lockout if the boiler does not start. Your problem could be the solenoid operated fuel valve failing to admit fuel or soot on the photocell that "sees" the flame so the controller "knows" the burner has started.

[Dave Liquorice]

seconds or

Not so sure from the OPs description. I think the buzzing was a stalled motor of the blower/pump that freed itself a couple of seconds into the 3rd or 4th attempt. As you say the ignition doesn't fire until 10s or so of motor/pump running, you wouldn't get the noise from the ignition at switch on.

[cynic]

You have not given any indication of what type of burner you have but the Thorn ODY is an early downward firing model and most used a Selectos D42 burner. The buzzing could be due to failure of the motor to spin and this can be a number of things. First of all does the oil pump turn smoothly and freely by hand or does it feel stiff? The motor has only a low starting torque at the best of times. Secondly does the motor also spin freely by hand or can you feel "cogging" due to a bearing giving up the ghost? Thirdly If both the above are ok you may have a failing starting capacitor which does not give enough start "oomph". Fourthly it is possible your burner sequence control is defective and may be misreading the phocell and not starting the motor. If the cell has low resistance the box can think the flame is lit before it should be in which case it goes to a condition known as false light lockout I'd be looking for a stiff oil pump and possibly fuel starvation due to a partial ice plug. One other thought comes to mind - has anyone tightened up any motor or oil pump mounting screws whci would compress the flexidrive coupling?

[cynic]

The majority of burner sequence boxes do actually energise the transformer early in the cycle. Riello don't but I doubt if its a Riello burner on this old boler

[Tom]

The boiler is now fixed. The shaft was a bit tight and the capacitor original and possibly failing so a new motor was fitted and all is well again. For the record, it is a Selectos D42 burner with a Petercem MA 28 AL control box. Thanks for advice and hints. Now I've just got to weigh up the govt's offer of 400 quid against a replacement. Tom