When I put the hot water on only, the water pipes rumble as the hot water from a back boiler rises to the indirect cylinder in the loft. When I switch the central heating pump on the noise disappears. Whatdo you think is the cause of this, and how can I cure it.?
Sound like kettling, the pipes may be abit furred up - limescale etc. With the heating on - the pump runs - so some heat is taken away for the radiators - the rest will be forced round the primaries.
You could try adding a cleanser/descaler, replace pipework etc.
But if you have a limescale/sludge/debri build up, it'll be in the heatex, tank/cylinder coil. Best bet would be to put you money towards a new system, instead of trying and possibly failing to rectify problems on your current system.
However as long as your water isn't too hot - boiler stat is working correctly. It may be a nuisance - but it's not dangerous, if you can live with it - it gives you time to save for an upgrade.
Is it a gravity hot water system? i have had blocked anti-gravity valves causing problems before (just a possibility as you may not even have one fitted) apart from that, htg eng has it pretty much covered
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