help with baxi condensing boiler

Postby carolmcc » Mon Apr 07, 2008 8:30 pm

I have a baxi 105e condensing boiler.
About 3 mths ago a B/G engineer came an replaced the diaphram, (think thats what it was called)since then the pressure has been really irratic sometime running at 3.5.

If that wasn't bad enough, everytime the hot water was used the boiler made a terrible noise (which has subsided quite alot).

But the annoying thing is, when the heating starts up, the water drips out of the overflow pipe. This in turn has started to to drip though an air vent and has started to drip inside rather than out. :(

Have had a B/G service engineer out again who tells me my system needs flushing and they do it for £650. :shock:

He said all the trouble i'm having was because of sludge and debris in the system, yet when he tested it the water was clear.

The whole system is 4 yrs old, does it really need flushing?? the first engineer said no..

Any advice would be appriciated.
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Postby ianr » Tue Apr 08, 2008 8:19 am

Sounds like two problems, firstly the filling loop (the tap on the bolier with the flexi braided silver pipe) is in the on position hence the over pressure and venting over flow pipe, the system should be filled to 2-3bar and then the filling loop should be turned off

Secondly there is air trapped in the system which needs to be bleed out hence the noise, non of these mean the system needs flushing though it would be cured by flushing because the system is bleed at the end of a flush.

The reason the filling loop my be on and air is in the system is the work done resulted in a leaking joint which your plumber could not motivate him self to find and fix, so leave the filling loop on, take the money and be on his way may of been the choice of the day

£650 would be the cost of installing a new boiler in most instances so it sounds like you spoke to the wrong plumber best advise is to avoid such people where possible.

Hope this helps
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Postby carolmcc » Tue Apr 08, 2008 6:01 pm

Thanks for replying.

Have checked the filling loop/tap there is no leakage into the system.

Also it was a British gas engineer who came out and I don't pay them for repairs as I'm on a flexi plan.

The pressure is currently running at 2 bar, which i suppose is normal but it still drips out of the overflow pipe.

The noise only starts when the hot tap is turned on, but like i said it is alot quieter now.

Its the dripping outside that is really getting on my nerves. If you have anymore suggestions it would be greatly appreciated.
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Postby htg engineer » Tue Apr 08, 2008 6:47 pm

No it doesn't need flushing. The drips of water from the pressure relief could be a few things
a) the pressure relief valve is passing (Most likely) replacing is easy
b) the pressure is too high (should be between 1.0 and 1.5 when cold)
c) the filling loop should be disconnected - not left where it could pass causing pressure to rise.

The noise could be and is quite common on the baxi Combi's - which is the diverter valve sometimes can just be an 'O' ring needs replacing. Normally a high pitch squealing sound - is that the sound you mean ?
htg engineer
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Postby carolmcc » Thu Apr 10, 2008 10:14 pm


It's really hard to explain but, then noise is a whirring sound which goes off after a short while.

The pressure fluctuates sometimes normal, sometimes high.

The dripping only occurs when the heating starts up, then it stops.

The noise isn't there constantly but it does come back when you turn the hot tap on, not for long though.

AlsoI have the hot water temperature knob on the off position but the water still gets hot.

gremlins in the works. lol

Sorry it took so long to post. Thanks carol
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Postby Bob Walsh » Fri Dec 18, 2009 10:31 am

Condensing gas boilers have been on the market for about twenty years now. The early boilers were noisy and very heavy. Today's condensing boilers are not even remotely the same as their predecessors. There have been many improvements that make these boilers lighter, safer, and more reliable than ever.
Condensing boilers are the most efficient way to heat that there is today. The BTU's that they wring out of the fuel put into them is the best of anything available today. Not only do they burn their fuel very well, they also have technologies built into them to help give then the highest efficiency possible on any given day.
Many of today's condensing gas boilers are controlled by a computerized control that gives many options and features to customize your boiler to the type of system that it is being installed in.

Greentech are specialists in a range of Condensing Boilers Services.

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Bob Walsh
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Postby boilergasman » Sun Dec 21, 2014 7:31 pm

Hi Guys

Kind of funny all the expert advise here....
First problem :high pressure:most of the combi systems are seald ones. As we are putting the heating on as a normal phenomenon the heated water will increase in pressure. There is a so called expansion vessel in every combi boiler, that compensates that expansion. In case the vessel is old or un serviced, its unable to compensate the heaTEXPANSION, meaning that the pressure in the system will increase over 3 bar, and the so called prv=pressure relief valve will open and release the excess water. When this happens its very common for the prv to catch small rubbish, and after it wont close properly.Solution:simple=service vessel, clean prv.

The high pitched sound is an o ring in the diverter valve that is old and swollen, that causes the terrible noise. If you take the cover off the boiler you can actually identify the direction and the source of the noise. Bottom left part of the boiler. Im just about to sort my one out (have the same problem), in case there is an interest, I can supply the part number of the o ring that needs changing.

good luck
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Postby htg engineer » Mon Dec 22, 2014 10:57 am

The noise could also be from the expansion vessel, if the pressure is rising only when the boiler is in use and discharging to outside.

Check the Schrader valve on top of the pressure vessel. If there's water the vessel needs replacing, if there's air or nothing then you might be able to re-pressurise using a foot/hand pump.
htg engineer
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