Noisy boiler - "Frying Tonight"

[Bruce Hall]

I have a Vaillant Economax 226E condensing system boiler which is 7 years old. The boiler is on a fully pumped sealed-system.

The boiler has recently started to make a crackling sort of "frying" noise when in "Hot Water Only" mode. The Vaillant engineer has attended twice. He first changed the pump, which made no difference. He returned two daya ago and replaced the heat exchanger, which has reduced but not eliminated the "frying" sound. The engineer said that if the new heat exchanger doesn't fix it, then the system will need flushing - he implied power-flushing.

The strange thing is that when the radiator heating is running, there's no frying noise at all - it occurs only when the HW circuit alone is on. I notice that if I have run the rads the day before, the boiler crackles when in HW mode the next day - if I haven't run the heating the day before, the the HW mode does not produce the crackling noise.

I've always regarded power-flushing as a bit of a con, especially when it comes with a =A3500 price-tag, so I don't want to go down that route.

Would anyone have any suggestions, please, as to where I go from here?

Thanks all,

Bruce

[john2]

Is this a hard water area. My boiler crackles when it's scaled up a bit, but its not a problem until it start banging as well.

john2

[Bruce Hall]

Yes, it is a hard water area - but the boiler heat exchanger is new, as is the pump. It still "crackles"...

Whatever it is in there, be it scale or flux, makes the crackling noise only when heating hot water - not when the ch circuit is in action.

Rather than spending 500 notes on a power-flush, I'd rather know what the consequences of doing nothing are.

Cheers

Bruce

[marvelus]

Have you considered trying a chemical flush? It is DIy and about £20 and to my mind if the coil in the cylinder is clogged up this might clear it better than the power flush.

[Bruce Hall]

That sounds a better option than 500 quid. The hot water cylinder is the same vintage as the boiler itself. (7 years old). Would it have clogged up that quickly?

Thanks for the suggestion.

Cheers

Bruce

[Ed Sirett]

Which heat exchanger did he replace? The main one or the secondary one that heat the DHW.?

[Bruce Hall]

main (primary) heat exchanger in the boiler itself is the one that was changed. As far as I know, the "secondary" heat exchanger that you talk about is the copper coil full of superheated water, an integrated part of the hw copper cylinder. The hw cylinder is the same vintage as the boiler - 7 years old.

Cheers

Bruce

[marvelus]

If there was no inhibitor yes.

[Ed Sirett]

Sorry this is the system boiler version. Anyway that gives a load more scope for problems, something is restricting the flow of primary water. A build up of crud on a balancing valve would be a possibility.