Apollo 15/30B PROPANE

[tectak]

Hi, Before the house blows up can anyone tell me what is causing the "exlosion" in my boiler on flame-up!
I recently came home to find the pilot light out. I checked it and it needed a new assembly as the pilot flame guide had disintegrated after 15 years. The relacement was easy and I serviced the boiler at the same time. checked for leaks with a radio-active sensor leak detector. OK.
System fired up beatifully and works well...........BUT. if switched off for a long time there is an ear shattering bang when it fires up!
HELP
tectak

 

[Agile]

Sounds to me as if you have a leak or the pilot is partly leaking or its just igniting the main burner late.

Tony

 

[tectak]

Hi Tony,
Many thanks for quick response. I am still alive. Yes, I agree that there MUST be a leak. The gas is presumably filling up the space below the burner. I haven't tried to see what happens iif I leave JUST the pilot burning for a long time.......if the gas mixture buids up to the level of the pilot light I can expect a very loud bang. What puzzles me is that the copression gland on the pilot pipe connect (with the olive) is fitted and tightened with PTFE around the threads. There is no sign of leakage using detector liquid or my hydro-carbon detector, though I suspect that the leak must be very small as it takes at least twelve hours to build up to the point where the whump occurs. I will have another look. Could gas escape from around the pilot jet without igniting in the pilot light flame?
Thanks again

 

[Jezzy]

get a CORGI to look at it. i'd do a test at the meter with your pilot light off. if the manometer is showing a drop, you have a leak somewhere on the system. if possible isolate all other appliances whilst doing this test.

 

[tectak]

Hi Jezzy,
i know you are right but the last two CORGI engineers left the boiler much worse than when they came! The first one set the gas pressure way too high for propane after admitting he didn't know WHAT the correct pressure was....honest enough. The second said the first was rubbish and left the system with such a bad leak at the pilot coupler that we had to leave the sytem shut down (constant explosions on flame-out) until a gas board friend came out and made it safe. That was three years ago and it has been fine ever since, with a yearly service and clean by me!
There MUST be a leak on the pilot connector somewhere....is PTFE the vogue method of sealing gas connections?
regards,
tectak

 

[Jezzy]

There is a special GAS version of ptfe tape but i wouldn't use it. What kind of a connection is it? i might use it on a compression fitting as a last resort. Use gas paste. Do you have a gas meter? Or is it bottled gas?

 

[pannierstan]

You might just find that the pilot needs cleaning or the topsocket needs replacing.

Stan

 

[tectak]

I am not sure whether this is a reply to Agile or Jezzy. Thanks to both.I tried a manometer drop test and using a digital (.01mBar) pressure gauge. The leak is so small that nothing discernable showed in 5 hours. In fact, the digital reading went up due to expansion with temperature!
However, as the fitting is with an olive I will get some gas paste and really give it my best shot. The pilot jet holder is brand new as previously mentioned. I am noting that the "explosion" is getting less violent as time goes by. Hopefully this means that the leak is sealing up with the crap in the propane (bottled) gas!

 

[garethgas]

A pressure test has nothing to do with your problem. It doesn't test after the gas valve.
My approach would be to turn off at mains, remove cover & soapy test the pilot assy. If all's well, I'd suspect that the pilot is too small or not aimed over the burner properly. As its LPG, double check you have the correct pilot assy too.
Let us know how you get along

 

[tectak]

Thought that would get your attention!!! Thanks to all that replied. Problem sorted! I found that the jet assembly when pushed into the NEW holder had a tiny piece of carbon or some such material preventing it from slding completely home. As a result, ther was a miniscule gas leak from the BODY of the jet. Every now and then it would pop very slightly when the cover was off and the outside draught blew the pilot about. With the cover on, no draught and so the gas just fell into the bottom of the firebox and built up until a firing up occured. During running I can only assume it was drawn up with the main burner updraught.
Thanks again,
tectak

 

[ollski]

There MUST be a leak on the pilot connector somewhere....is PTFE the vogue method of sealing gas connections?

On LPG and inside the combustion chamber??....no.