Central heating system de-sludge or just heat-exchanger de-sludge?

[Don Rojo]

My home central heating system uses a combi boiler (Brittony Combi

80). I think the secondary heat exchanger is starting to get blocked because the heat and flow rate of the domestic hot water is becoming a little erratic. I understand the hot tapwater is heated by the central heating water via the secondary heat exchanger. Rather than just remove the secondary heat exchanger and addempting to desludge it, I'm wondering if it would make more sense to desludge the whole central heating system. I'm thinking that if I desludge the whole system, then the secondary heat exhanger will get desludged in the process (apart from the channels that the mains water flows through, of course, which is probably clear anyway. Anyone agree?

I did the desludge process about three years ago, using a Fernox desludge solution. I left the stuff in the system for a couple of days then flushed it out and refilled with fresh water plus the standard Fernox additive. Should it need doing again by now?

Many thanks for any advice.

Don

[Christian McArdle]

I would have thought that it was precisely the mains water flow channels that are the problem. The CH side should have inhibitor in it and the calcium will have settled out long ago. The mains side has fresh calcium rich hot water, just ripe for depositing limescale.

Christian.

[IMM]

After 3 years the primary sealed side would need another dose of inhibitor.

[Christian McArdle]

But if the system has been operating correctly, without frequent refills, 3 year old inhibitor is likely to be working well, and sludging is unlikely to be the cause of the problems. Obviously, flushing and replacing inhibitor every 3 years is a good thing. It's just that the DHW side of the exchanger is more likely to have scaled up.

Christian.

[R Taylor]

diverter valve ?

RT

[Pete C]

Hi,

I wouldn't have thought the flow in the CH circuit would affect the flow of the DHW. Sounds like there is a blockage in the DHW part, maybe try descaling the secondary exchanger first?

cheers, Pete.

[Don Rojo]

Thanks to everyone for the suggestions. I think I'll try to descale the secondary heat exchanger.

I've been getting a lot of air pockets sputtering and blasting out of the hot taps when I turn them on. What might be the cause of that?

Thanks again,

Don