ISAR 35HE backfiring?

[jonesthesteam]

I've got a 2 year old ISAR HE 35 boiler which to be honest has been nothing but a problem since we've had it! The biggest problem we have at the moment is that when the hot water is run there is a large audible bang from the flue (louder outside than when inside house) much like a car back firing, and the boiler will produce hot water, but only if the taps are run slowly. When having a shower the water is hot for a while, then becomes cold, then after a while heats up again.

Any ideas folks?

 

[davebgas]

Does that 'bang' only happen when the boiler first ignites? Or is it a continous banging?

 

[jonesthesteam]

only when it fires up, but not always instantaneously, sometimes you can hear it after the has started whirring away, about 5- 10 seconds later. Also you can hear it when the boiler fires up occasionally (I preume to keep the heat exchangeer hot enough?)

 

[davebgas]

Could be the fan as a few of these drone like an elephant undergoing surgery...... gas valves can stick as well causing a bang on ignition, insulation pad coming loose obscuring burner, blocked condensate etc etc.... have an engineer come in to have a look at it.....

 

[jonesthesteam]

thanks for the quick reply, I'll sort out an engineer to visit before the onset of winter!

 

[davebgas]

Make sure he checks the ionisation probes in the combustion chamber are the correct ones and they arent warped.....

 

[jonesthesteam]

now it's starting to sound like the starship enterprise! Will pass the message on though!

 

[davebgas]

Just a loud droning is it???? Fan and or blocked trap/sump

 

[jonesthesteam]

no - much more like whir - BANG then all is fine apart from the water is only hot for a little while

 

[scatmanjohn]

Last one i had doing that needed a gas valve but heh its an isar so could be a whole list of things

 

[jonesthesteam]

so they don't carry the highest reputation then? The other option was worcester Bosch, now I'm starting to regret doing the budget option!

 

[Deleted member 105431]

so they don't carry the highest reputation then? The other option was worcester Bosch, now I'm starting to regret doing the budget option!

let that be a lesson learnt!

 

[gas4you]

The spark electrodes need checking first off.

You also need to have the working pressure at the gas meter checked professionally.

These boilers don't seem to like it if the gas pressure is low.

 

[davebgas]

They dont mind it..... if memory serves its a 1:1 gas valve so will operate ok down to 14.5mb inlet pressure...... dont shoot me if Im wrong, just trawling my memory archives

 

[gas4you]

I agree in theory they should be ok, but I have had numerous Isar/Icos 'faults' that have turned out to be low WP.

Even one of the Ideal engineers on my patch warned me of this