baxi burmuda rg3 screeching noise

[wouldbplummer]

hi there. i have a problem with my baxi back boiler witch has started making noises like an old kettle boiling behind it when it first starts from cold theres no sound then as it starts to get up to temp it starts this screech whistling sound if i turn boiler off mid way throu you can hear gurgling and sounds like air pockets which i guess is bad. this all started after i installed a heated towel rail and had to drain some water out of sistem ive re-bled all rads and there is no air in sistem only behind the boiler, so any idears on how i can get this air out there is a drain at back of fire/boiler which ive undone and drained two buckets of water out to try flush air out all the time sistem is refilling from vented tank in loft. does this sound like air to you or could it be lime scale would a inhibitor help if added. please help. also this is just an idea if i stuck a hose on drain is it poss to back flush air out?. thanks for listening.

 

[keego]

I had a very similar experience with my own boiler after fitting a towel rail. The boiler was kettling & very noisy, don't ask me why but it was all down to the towel rail, when I took it down to tile behind it the noise gradually went after a day or so.
Try shutting it off from both valves & leave it for a couple of days to see if it cures it.

 

[wouldbplummer]

ok ill try that if not im going to stick some fernox restorer in with some noise silencer that should do the trick

 

[wouldbplummer]

anymore ideas from the great diynot forum expert team come on someone knows something to try?

 

[Slugbabydotcom]

Boiler kettling

If a boiler is kettling its because the water is not flowing quickly enough through the heat exchanger. The temperature increase is too great in one pass of the water so it literally boils creating the noise.
To remedy it you have to think of things that would slow down the flow or cause the excessive build up of heat within the heat exchanger.
Heres a few ideas.
Sludge/scale in the boiler ... Remedy = fernox system restorer or similar as you suggest. If that doesnt work a chemical powerflush and if that doesnt work then your heat exchanger and or pipework is probably seriously crudded up. I did come across one case where a pumped 22mm Flow and Return to a cylinder was effectively reduced to 15mm by a coating of crud and this was in a soft water area!

Boiler not 'cross flowed' ... Boilers tend to kettle less when there is an even flow of water through them but the design of most boilers is a progression of the old solid fuel type. This is not condusive to an even flow resulting in slow moving water in areas not directly between the flow and return pipe. So even though the boiler may be correctly 'cross flowed' with the water flowing for example from bottom left to top right the remaining 2 corners dont have much movement of water. Worth mentioning that some boilers kettle even if they are fitted in accordance with instructions. My own Thorn Olympic, circa 1983 is a prime example

Inefficient pump. This only applies to boilers which are in a fully pumped system. Remedy = Turn the pump speed up or renew the pump if its on its last legs.

Poor gravity circuit ... If a gravity circuit is undersized or not constantly rising to its peak or has excessive horizontal runs [often unavoidable] then the water will not flow quickly enough. An airlock in the pipework would reduce the effective bore of the pipe and therefore the flow would also be reduced. Remedy = Check pipe sizes and that pipes constantly rise as much as possible from the boiler and there is nowhere for air to gather. Consider conversion to fully pumped system.

Faulty boiler stat. If a boiler stat is faulty or the probe is not fitted correctly in its pocket then it cannot sense the true temperature of the water in order to turn off the heat quickly enough resulting in boiling/kettling.

Pump over-run stat / wiring problem. [Not applicable in this case but I'll use this post as a draft for the FAQ section seeing as I have got this far!] A lot of boilers have a pump over-run device which circulates the water after the burner has shut down. This is to remove the residual heat within the heat exchanger that hasn't yet got through to the water after the burner goes off causing kettling or an overheat situation. Remedy = replace faulty over heat stat/device OR When wiring to a Y or S plan diagram the boilers wiring instructions should also be checked as the pump should be fed its current through the over-run device in the boiler

 

[wouldbplummer]

thanks for that some great advice,dont think its the pump coz its running on number 2 setting at mo when i turn it up to number 3 when boiler starts to make noise it doesnt change the sound one little bit, as for the faulty stat or probe where are these on my boiler? are thay anywhere near heat exchanger? could i change myself. thanks again for you help this is a great forum.

 

[wouldbplummer]

just to let you helpfull lot know that ds-40 done the job treated boiler only for 24 hours then stuck some noise reducer in plus protector lots of messing about wit draining and flushing but seems to be ok cost me about £50 and a day of messing about wit air locks (great).