Oil boiler - intermittent lockout

[Cold_James]

Hello,

I have a Danesmoor Utility 15/19 oil boiler with B9B burner and Satronic TF830.3 control box. Boiler sited indoors in upstairs room with outside tank lower than boiler, so Tigerloop fitted. Filter at tank and before boiler. Over 500l of oil in tank.

It had annual service in November - two visits, with changes made including:

Visit 1: new nozzle, tune up, clean and filter checks, new pump with coil, new motor (noisy bearings), new photocell (old one faulty)
Visit 2: new Tigerloop (old unit had failed with oil in upper chamber)

When the boiler runs, it runs very smoothly without problems, and can run for several hours. However, prior to the service, there was an intermittent lock out with the boiler locking out every other day - the engineer has tried to resolve this fault at each service visit in November, but the fault is now worse than before, with lock outs happening at least twice daily. The boiler is programmed to come on for periods of two hours in the early morning and early evening - typically it has locked out when period starts or on first start of programmed period.

Engineer not currently returning calls. Hoping to narrow down cause of fault to get heating running again before it gets colder.

If locked out and there is demand - I press reset on the control box, boiler motor and pump starts, ignition transformer can be heard (and flicker of sparks seen through peephole). Click of oil pump valve is not heard - but magnetic field detector held against coil very briefly lights (under a second) before boiler locks out. No evidence of oil in blast tube or nozzle tip

It typically restarts on second reset - same start up sequence, but click of solenoid valve heard (magnetic field detected and sustained, voltage pen senses increases in voltage from control box to solenoid), flame sustained.

Pump (BFP 21 L3) pressure starts at c100psi, tends to settle at around 92/94 psi with no obvious impact on operation - this is the same when it locks out as when it runs. A little foam in bottom chamber of Tigerloop on first start but reduces to none/very little on longer runs. Causes minor fluctuations in pressure reading but doesn't affect flame establishing/being sustained) and has run on this setup for many years.

I have checked resistance of solenoid coil (071N0810) across bottom two terminals (not open circuit hot or cold), and I have checked resistance of new photocell when covered and exposed to light (significant change - although couldn't find typical resistance for MZ 770 S). I have tried starting the boiler with photocell covered, photocell exposed to light, and normal with cell covered after ignition - in each case, it causes the boiler to lock out as expected.

Is the start up sequence:

Pump/motor and ignition transformer start together
Coil energised and oil valve opened
Photocell either senses flame or does not sense flame, leading to lockout

If so, my thinking is:

- no issue with oil supply (plenty of oil, new pump and motor working correctly, pump pressure set by engineer and same as when runs without lockout)
- issue seems to be either the oil valve not opening when energised or another fault causing oil valve not to open, leading to lock out as no flame established
- could it be another faulty new photocell (and is the photocell active prior to ignition?) Disconnecting photocell on next reset could rule this out if same problem experienced and boiler does not ignite?
- could it be faulty new coil/valve - and would it cause such an intermittent fault given new, fault occurs when coil 'cold'? But no problems with coil resistance, or operation of valve generally.
- could it be failing old ignition transformer (over five years old) - can this affect opening of valve/would it cause lockout so quickly?
- could it be failing old control box (over five years old) - do these tend to cause intermittent faults or just fail?
- could it be faulty electrical connections at control box, causing intermittent fault when cold? I can quickly check these with mains supply disconnected.

Not sure how best fault-finding process to take next to narrow down cause of fault, and avoid simply replacing parts.

I would welcome thoughts. Apologies for long post - don't want to waste your time so tried to provide all I know up front.

Thanks everyone.

 

[Burnerman]

That’s a brilliant explanation and your understanding of the system is very thorough!
Naturally the magnetic field must be maintained for the oil valve to remain open, any failure here will cause lockout.
As far as I am aware, it’s only the control box that does this so if it was mine, I’d fit a new one......assuming that all electrical terminals are tight.
The Satronic is a good unit, not renowned for failure but they are cheap enough.
A couple of things I would say....
The oil pressure should immediately register and maintain pressure ( shouldn’t yours be 100 psi?)
Don’t overtighten the grub screws that hold the pump to the burner - this can cause the pump to stall when starting up.
John

 

[Cold_James]

Thanks John - much appreciated

Re the valve - when tested it was showing c60v from control unit if measured at plug to coil with plug disconnected. I've only been able to measure with voltage pen when connected. Pen suggests lower range voltage upto post flame establishment then higher afterwards.

Regarding the oil pressure - the pump and pressure has been set up by the engineer. I have a suitable pressure gauge (from nerdy hobbies!) which I put in the P plug of the pump. From reading the manual, I think it should be 100psi - it is initially 100psi. It then fluctuates - between 92psi and 100psi as Tigerloop pulls air through. Oddly though it settles at lower pressure when all air derated and boiler has been running for a few minutes - nearer 92/94psi. There is no air being visibly removed at this point. I did wonder if this issue was causing the fault - but given it does also start when showing same readings I've assumed its not ideal but working! What can cause pump pressure to reduce and settle - I assumed only failing pump or air ingress - but new pump and no visible air ingress in Tigerloop? Presume bad idea to increase pressure without engineer as I may be affecting mix and creating more issues?

Re pump, engineer fitted the pump but all understood if I ever need to remove it - my understanding is the motor directly drives the pump? If so, no obvious stalling heard on failed start ups.

I will get new control box ordered - thank you. I'll keep you posted.

Btw daft question - I've seen posts referencing need for photocell to not sense light/stray light prior to ignition. But my understanding is the transformer energises from the start of the purging process. So, how does the photocell not read the sparks as light, or does the photocell actually only check from point that ignition is attempted (so its looking for appropriate sustained flame). It was puzzling me!

 

[Cold_James]

May be worth adding - the fittings/line from the tank to put it entered house were showing signs of leaking. Apart from valve at tank (as tank was full, the line, nylon filter and housing have been replaced using appropriate screw connectors and two compression fittings - appropriate compound used at joints and no signs of leaks. Pipe then continuous until filter housing before tigerlook and boiler. Engineer checked these when fitting new flexible lines and Tigerlook. So presume initial foaming is through air being pulled out of oil due to length of run/lift but foamy oil supply (and pressure fluctuation) is short-lived based upon visuals of Tigerloop (i.e. cleared within a min).

 

[oilhead]

If you can see spark through the peephole, then so can the photocell. This can give a false flame signal that causes lockout and stop the solenoid valve opening.

 

[Cold_James]

Thanks Oilhead. If so, what's at fault in that scenario? I looked at the Satronic TF830 instructions - it suggests the photocell doesn't trigger until the ignition phase, after the purge - but that the ignition sparks from the start of the purge phase (which is what I can see/hear).

That's why I am confused about the stray light issue - is the photocell actively checked by the control box prior to ignition? If so, how can it not detect the ignition sparking? It seems really key to my issue.

Thanks for your help.

 

[Cold_James]

I have checked connections behind control box - all tight. But engineer had caught photocell cable and an earth cable between screw and photocell body, flattening the photocell neutral and exposing the other earth. Will look to cut out damaged sections/replace when I replace controls.
Interestingly, since moving these wires, it has started to stutter on ignition - sometimes locking out, sometimes not. Magnetic field pen suggesting coil is energising and deenergising as the cause of the stutter. Think this still points towards photocell or control box.