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Boiler noise, any experts?
cliftyhanger - 1/4/21 at 06:43 AM

Got a Potterton Performa combi boiler, and it is making a loud humming/groaning noise soon after it fires up. It becomes a little quieter after about 10 mins, but is still comes and goes.
However, if I turn a hot tap on, the noise goes instantly.

My thoughts are that the heat main heat exchanger, pump etc are working with heating and hot water, so cant be either of those. Nor the DHW heat exchanger. So it must? be the diverter valve.... (pump runs smoothly if I touch it when running, but you can feel vibrations through te whole boiler when humming)
A kit to rebuild the valve is under £20, and as it is all water side I am confident to do this myself.

Anybody got any other bight ideas? plan B is a new boiler, but that is £1500....

joneh - 1/4/21 at 07:23 AM

Sounds feasible, if that doesn't work take a look at your pump as well, it may not being pushing the water around fast enough, causing a kettling type effect. When the diverter opens it lets more flow through and the noise disappears.

I had a valiant boiler that made groaning and kettling noises, turned out my pump had some swarf wrapped around the impeller, left in by my useless (ex) plumber, although it wasn't a combi.

Cannonball - 1/4/21 at 10:00 AM

We had our three year old Potterton promax boiler serviced and the next morning it was making weird noises. It sounded like the outer casing was vibrating. Turned out that it was running too lean or too rich. Can't remember which.

Mr Whippy - 1/4/21 at 10:11 AM

You often get a noise and vibration when a valve is only partially open, maybe its sticking and not able to open fully.

cliftyhanger - 1/4/21 at 10:27 AM

quote:
Originally posted by Mr Whippy
You often get a noise and vibration when a valve is only partially open, maybe its sticking and not able to open fully.


That is what I am beginning to think. Got to be worth a try for the cost of a rebuild kit.
I forgot to mention, I have also cleaned out the hot water heat exchanger. That was quite scabby/nasty inside before the acid treatment. And I have some cleanser circulating to clean some of the crud out of the system, with a magnetic filter to hopefully catch the bits.

I won't get to it before Tuesday, will remove the diverter valve then. How hard can it be (probably realise I need smaller hands)

gremlin1234 - 1/4/21 at 10:37 AM

most diverter valves have an 'override' mechanism, maybe try locking the valve open and trying it again. before you dismantle it

theconrodkid - 1/4/21 at 11:31 AM

try running it with the gas turned off, that will eliminate kettling.
mine did this, i went into the loft and found the header tank full of black sludge despite a new hot water tank being fitted only 6 months prior, drained the system, added inhibitor and it was 90 % quieter

Jordan - 1/4/21 at 07:18 PM

When was the last time it was serviced?

It could be the high /low Co ratio is out and needs setting

Heat exchanger, expansion vessel, condensate trap blocked?

If you got about 10 or 12 rads / one bathroom id be looking at a baxi 800 or something with a 10yr warranty can't go wrong for the money your looking at about £1500- £1700 supply and fit here in S. Wales.

mark chandler - 1/4/21 at 07:39 PM

Have you checked the expansion vessel is pumped up, it should have around 12 - 15 psi pressure with the system fully discharged.