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Strugling to diagnose problem on worcster 30 si

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Jonzo25

Right what happens is the boiler will be running as normal all of a sudden it will make a huge bang (enough to make me jump 5ft!!) My first thought was flue blockage or condensate, checked both and their fine, checked the Neg pressure was ok on fan it was at -5, cleaned out the baffles on heat exchanger and checked for cracks etc fine, check inlet pressure standing and workin both fine, had it running for an hour with no problems before i left today but recived a phone call 2 hours later of the customer saying it happened again when they opened a hot water tap. Being honest I'm at a loss as when it happend i couldn't even localise where the sound came from.
 
late ingnition, wrong gap on firing electrode. poor fan speed,
 
Thanks guys, Im not a massively experienced fault finder im usually just on the installing side, just doing a favour as its a friends boiler, what steps should I take now to rectify this?
 
Obviously the most obvious thing would appear to be late ignition for some reason. Doing an FGA would possibly confirm this but not perhaps tell you why it was late igniting. The ignition electrode gap may be to big as said. As may the fan be slow to clear any gas from the combustion chamber.

I know it may sound improbable but could it be something other than a gas explosion? It just seems a bit odd assuming in this weather the heating was running and the burner working to get an explosion when the change over valve called for hot water. But then what would cause such a noise other than gas?

Mind you sticky change over valves can cause noise. It may be worth a look if nothing else shows up.

Good Fortune
 
ive had that happen to me and gas valve was passing but that was on start up,,, have you tested the gas valve for let by
 
Most likely cause is the gas valve. Diverter can make a loud bang when moving up to HW from CH.

How old is the boiler? I have had a couple where the ignition electrodes warp.
 
Heating was on when the demand for hot water was made, not checked for let by on gas valve will do in the am, the boiler is 5 yrs old.

So could it be I need to replace th Gas Valve?
 
wrong gap on firing electrode.check have seen a few bent ones due to fatigue, then gas valve. if failing replace,
 
dont forget to replace burner gasket seal,as w bosch requires you to do every time you open it !!!

also if not sure give them a call great technical service !!!

but do remember on the way there in the morrning to pick up a seal !!!

and let us know how did you get on !!

you can do resistance test on both solenoid if they come different to each other ,there is your fault !!!
 
Sorry for getting back on to reply late been busy with work and festivities ;) Happy new year to you all!!

Checked everything as mentioned above and was still having the same problem, decided to take the heat exchanger apart again as I could hear a rattling, and the last time I turned it on the bang was ridiculously loud, as soon as I pulled the burner out i found the problem, the plate at the bottom had blown off and every time it fired up it was causing the bang!!

So yeah never seen that before and is a great learing curve for me as even technical couldn't help me with this one!!

Thanks for all your advice and help guys!

John.
 
by plate at the bottom do you mean the spring on the bottom baffle?
 
No it was on the bottom of the burner, the plate deflectes the flames from passing the burner and helps them brun equally allong the burner itslef. i have never seen this problem before.
 
When I did training with w Bosch they showed us cut in half burner which was burned out nearly melted , they told us this was the only rare case due to low water in system if I remember correctly !!!
 
SafeGasInstall said:
When I did training with w Bosch they showed us cut in half burner which was burned out nearly melted , they told us this was the only rare case due to low water in system if I remember correctly !!!
Click to expand...

if thats what they said GSI does that mean no LWP fitted same AS A BAXI 105 JUST A PUMP PRESSURE SWITCH MEANING WATER PRESSURE CAN GO VERY LOW and cause damage before the high limit stat kicks in and does its job,but in these circumstances i would think the main heat exchanger would give up before the burner

ignore CAPS KEYBOArd faulty
 
Last edited by a moderator:
sorry my bad it was a main heat exchanger that was melted not the burner just had a look on the flash drive they give me ,sorry !!!
 
that would explain it,but if that can happen then no LWP fitted,why do manufacturers do this?
 
this is a photo of good one

Picture1.jpg
 
As everyone else has said, the Air / Gas ratio is critical, if you haven't got an FGA you're wasting your petrol money, hopefully you have one. Once that is checked high and low I'd be checking if electrodes are clean. Seems that sometimes it's a process of elimination when diagnosing from afar.
Good luck
 
Haven't got a photo to upload sorry guys. Did a FGA and the results were fine, all sorted now got the new burner today and we have a warm and happy customer.
 
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