Baxi 105E boiler whistling when CH is on

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13 Feb 2004
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United Kingdom
We have a Baxi 105E Combi boiler - only around a year old. Whenever the heating comes on, after a few minutes it begins to whistle like a kettle. (like a kettle this noise increase gradually to a constant level) It seems to be emanating from (or around) the boiler somewhere, but here's the real mystery: it stops immediately as soon as you run a hot tap. Another symptom is that when you close the hot tap, there is a creaking noise then a light clunk from the boiler - this happens when and only when the heating is on. It also happens regardless of the whistling.

Any ideas of how we can solve this problem and get a good night's sleep?
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Your noise is almost certainly caused by either lime scale or sludge in the boiler the noise when switching from heating to water is the built in 3 way valve opening and closing water hammer behind valve seating very common on this model but noting to worry about
ahhhhhhhh! i was waiting for this problem to start again, i thought baxi sorted it as the baxi 105 boilers we fit are now not doing that

The noise is not lime scale or anything! it is infact a small black washer. under your boiler you have chrome fittings. locate the h/w one and the connection made to the boiler has a small black o shaped washer that jumps due to a small bit of dirt. This was a nightmare for us as all our baxi boiler where whisling. There is no problem with the boiler just the black 0 ring. If you get baxi out it will take them 30 secs to repair!

As soon as you run the hot tap the sound will stop, this indicated 100% its only the 0 ring washer!
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Am I reading you right? Boiler output HW connection has a washer/O ring which vibrates when there's NO water running through it??? :eek:
nope your not reading me right. Its a common fault on a baxi boiler i thought you might know that. although the heating runs it can cause a washer on the h/w to vibrate. When the hot tap is opened the washer stops vibrating which stops the whistle. I have repaired many of these and baxi had repaired this fault as the new 105 boilers dont whistle. Maybe its a stock boiler.

simply contact baxi and they will replace the washer, that is the problem.
Wow, thanks for the comprehensive (and quick) responses - much appreciated.

Potterton Man: I'm now much more reassured about the tap thing.

Boxster: Excellent tip - I suspect it is the sort of thing that might take someone who wasn't aware of the problem much headscratching and failed attempts to fix.

Really, thank you very much.
Sorry, still can't see it. Is the washer in the hw union where the copper connects, or further in, on the diverter?

Haven't come across one doing it yet. I do more installations than reps!
chris have you never had a baxi 105 that whistles???

i fit around 2 per week and we had loads!!! you know when you put the jig on the wall, then pipe the boiler up. when you re-fit the boiler on the jig and connect the last remaining chrome pipes to the boiler... have you noticed baxi changed the design slightly... its the H/W washer that is installed to connect the boiler to the jig. It something used to cause it to jump but baxi repaired the fault and sinse then its been great. Do you collect baxi points if you do ask the baxi rep about it.. he will let you have the problem repair report for future ref... :D
Boxter I thought the rubber washers were for Gas connection only. Fitted a few 105Es but bever had above mentioned fault. Last 105 install had two on the wall running a Megaflow 300 as well.
yer your right db it is, the one i mean is the washer going to the h/w, fibre washers one connects boiler to jig. I think its a little higher up tho. the baxi rep told us, its caused by knocking the flue out whle the jig is on the wall or the washing isnt sitting right. Baxi re-designed this have you noticed a big change in the jig..

hey also db and anyone else is this just me, but are you having trouble getting 22mm yorksire fittings on the baxi copper tails????
I also have a baxi 105e with what sounds like a similar problem. I just want to check its the same issue though...

When the CH comes on (and possibly off) there is a whining noise coming from the boiler - which stops when you turn on the hot water. This is the bit that sounds like the issue already discussed.

However, also, when the hot tap is turned OFF there is a different pitch whining for about a minute which slightly oscillates in pitch, making me think there is a valve opening and shutting somewhere.

Any ideas? I suspect that this is not something I should attempt to fix myself as an amateur but an idea of the problem so I am not stuffed by a cowboy would be good :) Many thanks.
The problem is that the divertor valve "o rings" have become oversized/stretched. The only way to cure the problem is to replace the "o rings". There are three "o rings" on the 105E and four on the Instant. Any heating engineer/plumber can fit the parts, though Baxi would probably be the best bet.
Just had an amusing experience. Had a (non-baxi) guy come out to look at it and told him what you said. He didn't think it could be that and started talking about a dodgy flow switch. Having taken it apart and saying it was probably that was in the process of ordering one over the phone. Not wanting to have him fit it only to find out it wasn't that, (which given I could here the microswitch clicking ok, I didn't think it was), I pointed out that we could test his theory by cutting off the switch and holding the wires together - he grudgingly agreed. Sure enough it wasn't that. He ended up phoning up Baxi who confirmed your diagnosis (to my concealed amusement!). So he didn't charge me for the callout - quite rightly. However I've got to try and get him back to fix the switch which IS now broken! I'm calling baxi out who say if it is the O ring thing then they will do it for free as its a boiler fault.
Now.... I think I'll find out how to get my corgi registration cos at £61 + VAT this is a nice game to be in. I did a masters in Chemical Engineering - how hard can it be! (OK, sorry, I'll stop being an arrogant twit in a moment ;) ).


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