Intermittent fault, Eurocal with Sterling ST108

[myles]

Got called out to a Eurocal boiler with a Bentone Sterling ST108 burner last week that I serviced last month (since found that the issue predates service, no ignition issue during service), Usual thing where it has an intermittent fault. So I arrive on Friday afternoon and the boiler wont light at all. I changed the electrodes as the ceramic had a big crack right across from one electrode to the other (prob from an over-tightened bolt) also changed the HT leads I had advised homeowner about this during service. Did usual elec tests, pump pressure, fan etc and everything seemed in order except it still wouldn't ignite. Apparently the boiler wouldn't light for the previous two days. I spent a bit more time double checking electrics for loose connections but no change. Looking at flow chart for the burner and it basically came down to a faulty electrode transformer. Had to go as it was getting on and homeowner said its fine as they don't really use boiler much! Anyway I ordered a new transformer and went back today, Called for heating and boiler lit up straight away without even touching it! Customer said boiler had been lighting fine over the weekend but didn't this morning. Then the next problem came where I tried replicating the fault of it not firing up so turned boiler off and on etc boiler ignites every time lol. Took the opportunity while it was running to test the thermostat which turned boiler on and off when turning dial up and down from 0 so far so good. Stuck fire-valve tester @60c and put thermostat phial in which shut the boiler off as expected (thermostat set at 50c). Turned thermostat up to 80c and burner went through sequence but wouldn't ignite and ran to lockout again so now thinking maybe the thermostat is faulty. Overheat stat worked so ruled that out, Photocell is fine with no obstructions and fga comes back spot on when its running (no change from when I serviced it) I then changed the fuse for a new one and boiler ignited straight away so again turned on and off by various methods and each time burner ignited without fail! Don't really want to be swapping out parts if its something simple that one of you guys has come across before! If any other oilies have any idea I would appreciate any advice via PM or whatever (don't want to many clues on here for DIYers) :dizzy2:

 

[SimonG]

Thermostat and lockout are not linked. Whats the combustion like when it is running? Check position of electrodes. Any damp in the control box?

 

[SimonG]

Went to a firebird tonight. Rdb burner, they have had problems since firebird came out last year at end of warranty. Flame dropping out and then firing back up. Photocell was about 1/2" out of its holder. Pushed it home and ran like a train. Easy money

 

[myles]

Combustion is spot on when its running, no damp in box that I could see, electrodes are within specified limits checked they were right with my calipers when I put them in, I was leaning more towards the control box but cant be 100% as its so intermittent!!!

 

[myles]

Went to a firebird tonight. Rdb burner, they have had problems since firebird came out last year at end of warranty. Flame dropping out and then firing back up. Photocell was about 1/2" out of its holder. Pushed it home and ran like a train. Easy money

I wish this one was that easy lol best I had was back boiler pilot not lit [emoji106]

 

[SimonG]

Try dropping the oil pressure and air a touch. Ive seen some were the fan blows the spark away from the nozzle, if tbat makes sense.

 

[myles]

Yeah makes sense, guess its worth a shot I'll see how its running now over next few days (going to service their shop boiler next week so will find out then) cheers!

 

[Best]

You could take a look at the spark at electrodes by disconnecting the solenoid & taking a look in the front of blast tube. Try it loads of times to see if soark ever suddenly gets weak or fails.
Control box can also be very intermittant - failing one day and working all the next day.

 

[Bunker]

Cause and effect.

You have to ask yourself why did the transformer fail? Its usually because the control box is chattering or keeping the ignition on for too long. Its also often caused by the photocell being partly obstructed or faulty - it sees the flame, doesnt, sees it, doesnt - every time ignition is initiated, the transformer runs for 12 seconds and will burn itself out. As you have changed the electrodes, check the view of the photocell or try running the burner with the pcell out, covered, then show it a torch after the coil clicks.

 

[Pipes Plumbing]

Have you checked that the photocell isnt dirty or damaged in any way?

Had an RDB3 doing similar recently, where sometimes it would start, flame out, start, flame out etc but only once in a while. Most of the time it would click into life as normal.
When I pulled the cell it turned out that it had a film of crap on it from where the initial butchers that had installed it had left the settings so far out. The end of the photoresistor itself was slightly offset in the rubber too, as if it had been rammed in against the side of the housing previously.
Cleaned and straightened it out and away it went. No issues since (plus the combustion setting are now right!)

 

[myles]

Yeah photocell is fine one of the 1st things I check tbh being as its a common problem. Havent heard back from them yet will give him a ring in a couple of days and see how it is going

 

[myles]

Went back today as it decided not to light yesterday swapped the transformer and much stronger spark now but still wouldnt light, opened bleed valve and boom no oil traced it to the fire valve which wasnt tripped but wasnt letting oil pass so was letting it through sometimes and closing off supply randomly! swapped valve and bobs your uncle! Did my head in as everytime I tested it before there was oil present! Funny thing is I advised changing the valve when I serviced it

 

[smitty1892]

Good to hear problem sorted , most common intermittent fault I've found with sterling's is the transformer. They seam to get a very weak spark over time , I always keep a spare for intermittent sterling faults .

 

[myles]

Yep weak spark before now it goes like a good un, I wouldn't fancy putting my finger near it lol! I think that somehow the old firevalve was randomly closing when the boiler turned off and then when custard tried to turn it back on yesterday it just pulled what oil was left out of pipework made it easier for me in a sense as I could diagnose it quicker!

 

[smitty1892]

What make of fire valve was it for future reference ?

 

[myles]

Was an old Teddington with the pin on the bottom I would say about 10 years old

 

[Best]

Was an old Teddington with the pin on the bottom I would say about 10 years old

The Teddington KBB firevalves (& probably all other types) are very small inside & block with the tiniest dot of sludge. They are something I am very careful about. I flush oil lines by removing the KBB so I don't get dirt in it & akso get full flow through the oil line.
As you said, the oil can appear to be flowing okay & the boiler running, but the line is blocked. Same with oil filters. The paper element filter fitted at oil tank does a great job to keep the oil line clean.

 

[Bunker]

Those fire valves cannot open and shut on their own, they are one or the other. Maybe it held a partial blockage or might be a red herring. Did you check tank filter?

 

[myles]

I recommended it was changed at service due to it not shutting supply off when tested I would say dirt is the most probable cause over time as the filters were dirty. Custard said it had been like it for a 'few years' but they dont use heating much as they have a log burner etc, I would say it hadnt been serviced in quite a few years. Definitely one I will remember though!

 

[myles]

Those fire valves cannot open and shut on their own, they are one or the other. Maybe it held a partial blockage or might be a red herring. Did you check tank filter?

Yes I serviced it and cleaned all filters previously, they were all still fine, traced the blockage to fire valve, it couldn't be reset by pressing button. I had checked it on previous visit to no avail. As with anything mechanical it can do things out of the ordinary! Guess time will tell, needed changing anyway!

 

[Dotty]

As it happens I had one on Friday with an intermittent fault, the young lad before me thought pump but when I checked I decided that there was no positive difference between open and closed on the KBB.

Replaced.

 

[myles]

I'll take this opportunity to thank everyone for their replies and input towards this post! I do wonder why there isn't a private forum for oilies like the gas safe one though? Anyway thanks again chaps! :rockon2:

 

[Bunker]

As it happens I had one on Friday with an intermittent fault, the young lad before me thought pump but when I checked I decided that there was no positive difference between open and closed on the KBB.

Replaced.

How would that create a fault - was it just very poor flow when open? Cheers

 

[Unregistered]

Geminox Astrane.Bentone ST 108 burner.Intermittently fires up and then starts 'chattering' for a couple of seconds and then locks out.Noticed that a lot of air bubbles collecting in fuel filter when pump is running.Photocell changed,control box changed,pump changed some time ago.This problem has defeated French plumber who installed it,so he won't attend anymore.(I'm in Brittany)Excellent boiler but this problem is doing my head in.Any good folk come across this before?

 

[SimonG]

Lot of bits changed, whats the pressure gauge read?

 

[lame plumber]

dont take this as criticism, but when servicing a boiler and you see something needs doing, why dont you repair/replace the part, because if you dont how can you say you have serviced the boiler, knowing its got issues that invariably lead you to having to go back to sort it out?

 

[smitty1892]

If you mean air bubbles in tiger loop , one of two things small leak on line or flexible oil hoses has a pin hole. Had one like this before .