Loud knocking from combi-boiler

[itzcold]

Our combi-boiler (Voker 20-80 RS Flowmatic) is making horrible knocking sounds when the CH is turned on (until it gets up to temp and the boiler switches off). I had BG round and they said the sound is "kettling" - it's scaled up and needs to be replaced.
I have a few questions:
1) Is it possible to de-scale the heat exchanger in a combi boiler ?
2) Why should it suddenly start knocking/kettling - wouldn't it gradually get louder over the years?
3) If the CH is a closed system surely there's only a fixed amount of limescale in the water, so how did it scale up?
Any help appreciated before I hand over a large wedge to BG for a new boiler.

[HSP]

check the pump!!!!!!!!!

also watch out with BG they are very crafty - they will hit you where they can!!!!!!

they should be using the term sludged up

The system water may never of had inhibitor or before the boiler was fitted the system was not cleaned so the sludge sits in the boiler
_________________
Dont cha wish your bouyfriend was a plumber like me !!!

[Agile]

Interesting question for the OP.

If BG have had the maintenance contract for a few years then they should have added inhibitor or chemicals to prevent problems like lime scale.

Tony

[itzcold]

Thanks HSP and Agile. There was never any inhibitor added as far as I know.
We've had about 5 different visits from BG over the past month. One of them replaced the pump, but it made no difference. Another repressurised the pressure vessel. Another changed a diaphram(?).

I've been hunting around for a local heating expert for a 2nd opinion. Trouble is, it's difficult to get an appointment - "its the wrong time of the year".

[Agile]

[HSP]

and thats very reasonable for london- cheeky buggers
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Dont cha wish your bouyfriend was a plumber like me !!!

[itzcold]

Well, now I have 2 much more reasonable quotes to replace the boiler. Both from Corgi registered chaps.
Problem is, one of them wants to replace the gas supply pipes with 22mm which sounds like a big job involving removing carpet, floorboards, tiles etc.
How do I know if that's really necessary ?

[Agile]

Anyone who expects to use a 15 mm gas supply for a combi is a cowboy !!!

Did you see their CORGI card in their own name or that of THEIR firm?

Tony

[HSP]

i can just about bet it will need 22mm upgrade!!!!

9/10 boilers i do needs a gas upgrade !!!

Like agile said only a cowboy would suggest it doesnt need it


i losyt a job because i was going to upsize gas main last night!!

obviously othe rfirms just going to use existing and not give a toss !!!!
_________________
Dont cha wish your bouyfriend was a plumber like me !!!