Remeha quinta very loud bang on ignition

[bright spark]

Called to job last Friday. Both boilers down. One had poor ionisation probe readings. Replaced the electrode on boiler and it ran fine. The other one when it ran to start, on ignition it made a very loud bang. I had loads of calls on so I told the customer I'd be back the following week. Am hoping to call tomorrow or Friday. Maybe the gas valve is going faulty releasing too much gas on ignition, but that's only a thought.
i was wondering has anyone had similar problems with this model. It's a quinta 65, not the newer 'pro'. Have worked on many remehas over the years and have not seen this before

 

[bright spark]

Or maybe there's a problem with the pre mix burner.
Im open to suggestions

 

[lame plumber]

or the other has poor spark so too much gas builds up before it ignites!

 

[bright spark]

No the boiler goes through the starting sequence, the fan runs, the second it goes to ignition (at stage 2) and the electrode starts to spark the very loud bang occurs. Thanks for the idea though. Will let you know how I get on before the weekend

 

[Billy Bob Bob]

No the boiler goes through the starting sequence, the fan runs, the second it goes to ignition (at stage 2) and the electrode starts to spark the very loud bang occurs. Thanks for the idea though. Will let you know how I get on before the weekend

what is your inlet pressure doing when it bangs?

 

[bright spark]

The standing pressure is 25 mbar. The remeha quinta brochure as far as I remember says it can operate in the range of 17.5 to 30mbar in Ireland anyway. I presume it's the same there.

 

[Billy Bob Bob]

The standing pressure is 25 mbar. The remeha quinta brochure as far as I remember says it can operate in the range of 17.5 to 30mbar in Ireland anyway. I presume it's the same there.

yes but what is it dropping down to at the inlet on ignition? are both boilers off the same meter or separate if the later could be a regulator fault

 

[bright spark]

Both boilers are off the same meter. They were both broken down when I arrived flashing 4 04. Fault in the past signal. Anyway I went to the right hand boiler first which ended up being the 1 with the poor ionisation current. Changed the probe and the running pressure on that dropped to around 23.5 on start up on low flame. I reset the left hand boiler and the fan started on low air and as soon as it went to stage 2 a very large bang came from it.
I knew it wasn't going to be a quick fix and to be honest I had a load of breakdown calls on my back from other commercial customers. I had some heat back on to keep the customer happy and decided I would return to fix. Hadn't expected the weather to b so bad that's why I haven't been back yet.
my own personal feeling is that the gas valve has developed a fault opening too much straight away. Anyway that's only a hunch.
Thats what I get for not putting the u gauge on when resetting the boiler I have to confess

 

[Millsy 82]

If it's a pre mix burner most gas valves are open or closed. I would look at high/ low co2 settings. I know I went out to a remeha a year or so ago with the same problem so checked and adjusted co2 first then it all worked fine.

 

[bright spark]

Finally got back to job. To cut a long story short. Took boiler apart, found that heat exchanger insulation gasket had perished slightly round premix burner. This led to gas/air mix entering the chamber through gap instead of burner tube being ignited with a loud bang. I changed the exchanger insulation gasket and all was quiet

 

[Petefinny]

These have a service kit which once replaced solves a lot of problems with Remeha's, new seals and ioinisation probes