Burner problem

[loughneagh]

Hi folks, I'm new here and would like some help please, I'm not a boiler guy I'm a M+E eng. and have always serviced and repaired my own boilers and those of my family etc.

I'm not getting voltage to the oil pump solenoid on my Sterling burner. I've tried a spare, (new) Satronics TF 830 with the same result, 62V, which just looks like a bleed voltage through the neutral. I've looked at the schematic and suspect that the "flame relay" in the controller isn't supplying the solenoid. The wiring all looks OK, the controller base seems fine and the solenoid cable bells out ok. The flame detector resistance changes with light, (but of course it shouldn't come into play immediately anyway). Is there anyway this relay can be at fault? It's hard to tell if the push contacts are OK but everything looks fine.

Any ideas?

Thanks

 

[martineire]

change photocell, if motor is spinning (pump/ fan) photocell looks for darkness first before allowing control box to energises coil and spark electrodes

 

[WDIK]

clearly the solenoid needs to open, never rmind daft advice.
check it with 230v

 

[loughneagh]

Thanks to both.

The electrodes are sparking and the solenoid does open with 230V, (new pump and solenoid). This is what I changed originally when I had no oil to the burner. At that time I checked for voltage at the coil and had 230V and checked the coil resistance, about 2.2K ohm from memory so suspected the mechanical part of the solenoid valve. Seems like there has been an intermittent electrical fault.

I had suspected the photocell too but it changes from about 80K ohm to about 1/2 a Megohm in garage light or shaded so seems to work in some shape or fashion. The schematic isn't clear, will the photocell hold the flame relay out if the resistance is too high or too low rather than being "on" or "off" over a fairly wide band?

 

[martineire]

clearly the solenoid needs to open, never rmind daft advice.
check it with 230v

and its never going to open if photocell is faulty

 

[doitall]

I assume you have changed the nozzle and cleaned the filter.

 

[Agile]

If the controller is not applying 230v to the solenoid then no oil will pass and the condition of the filter and nozzles will not be relevant.

The resistance values of the photocell sound about right but I dont work on many oil boilers. Check the photocell leads and if OK then you could try substituting a fixed resistor of say 1 M Ohm might encourage it to momentarily open although it will then shut down after a few seconds as a low resistance has not been provided as expected when the flame lights.

Tony

 

[loughneagh]

Thanks Agile

The photocell cable belled out OK, I've bought a new potocell to try tonight, I'll let you know, if not I'll try the resistor trick. Is the controller looking for a fairly specific resistance? As you say it seems about right and is changing resistance with light but perhaps it has drifted outside the required parameters?

Cheers

 

[Agile]

The controller assumes over a certain resistance is no flame and less than another resistance is flame.

I dont think those fixing boilers bother measuring the dark/light resistance they just fit a new one. They often need to replace them but no one ever gives me old ones to measure.

Tony

 

[martineire]

Yea if a photocell is suspect just replace it, its only a few quid for a new one. unless you have a lux meter to test the value of the suspect one.

 

[loughneagh]

Martineire/Agile

Photocell did the trick, the boiler fired up first time. I should have done the laymans thing and just stuck a new one in at the start but I like to know why things don't work and then pickle my own head!

I can only guess that the cell was breaking down or resistance has drifted out of normal, the boiler has been a bit temperamental of late when I've been away for a few days, switched HW off and turned the room stat down, often the boiler has locked out when I've got back. Maybe when the boiler, and therefore the cell, have been warm there hasn't been a problem but when off for an extended period of time damp or cold has affected the resistance? Anyhow, it's working now and thanks for your help.

PS. the new oil pump I fitted has a variable pressure, any tips on where to set it or suggested pressure?

Cheers

 

[Agile]

It needs to be set with a pressure gauge to the recommended pressure to be used with the fitted nozzle.

Then the flue gas needs to be tested with a flue gas analyser to check the combustion is correct.

Since you can do it, could you test both photocells under dark/light conditions and tell me the resistance found to see if it could have been identified from the resistance. I only go very infrequently to an oil boiler and dont carry spare photocells.

Tony

 

[loughneagh]

Ha, you think like me! I wondered the same thing, unfortunately nothing clear cut. The original photocell is about 50-60K in garage light and is just about making infinity when covered, the new one (MZ770s), is around 40-50K in garage light and easily makes infinity when covered.

When I was fault finding I hadn't unplugged the cell, just covered it to make sure that resistance was changing with light, which is why I only got the 1/2 Meg. It can only be break down with voltage, the old one is a fairly ropey looking affair and is more like two bare wires on a pcb than the nice new properly sleeved unit.

All I can suggest is that as the new cell was only £6, stick one in your box and if you're not getting oil then try it.

The nozzle only states 0.65, 80oS, which I think is US Gal and degrees? It's a 22kW boiler using 28sec oil but no pressure markings. I can easily put a gauge on it if I knew what pressure I'm looking for but I have no way of doing the flue gas analysis, I may bite the bullet and get a boiler guy out to set it up for efficient running, (much as it galls me to)!

Cheers

 

[martineire]

Glad its sorted, what make boiler is it tho you just said its a sterling burner and said its a 22kw boiler, and then ill tell you manufacture setting for your boiler, but they will just be manufactures setting (factory set) your burner will still need reajusting to suit on site conditions and a flue gas analyser, smoke pump, oil pressure gauge will be needed for that.

 

[Agile]

All measurements on components have to be done when disconnected from the circuits of the boiler.

You are both in Ireland!

Pperhaps you are close to each other?

Tony