hot water pumping up through expansion pipe when valves off?

[andyr123]

Hello I just want to ask the question on average how long are we talking in months or years for radiators and central heating pump to get damaged by oxidation when oxygen enters the central heating through the C/H cold water header tank in the loft? - at the moment if the copper immersion cylinder is satisfied with heat (60c) and the zone valve turns off and when the radiator zone valve is satisfied that shuts off - if both valves are shut off i can hear the water trickling into the cold tank in the loft, if at least one valve is open then i cannot hear it pumping back into the header tank, so it only pumps back into the cold water tank through the expansion pipe when both zone valves are shut and pump still going (oil boiler off at this stage because it has reached temperature) - i know its not ideal this way and oxygen will be getting into the system and I've heard plumbers say this will eventually damage/rust the pump propeller and the inside of the radiators if this is happening, but im just wondering how long roughly that damage will take? Thanks.

 

[JohnD]

weeks.

Steel + water + air = rust

Do you know the cause, and how to fix it?

How long has this been happening?

 

[andyr123]

weeks.

Steel + water + air = rust

Do you know the cause, and how to fix it?

How long has this been happening?

thanks been like this since around sept/oct since had rads on, had noticed the immersion tank stat on 80c but the boiler to 60c so the zone for the hot water would have always been open, but i put boiler to 65c (now im running rads) and cylinder stat to 60c so when both satisfied both valves shut and water pumps to header tank. when looked at zone valves, i suppose if i culd find a way of wiring up pump to stop pump when both valves closed (and boiler not iring up) it would eliminate it pumping into the header tank. The cold feed is on the return and the pump s on the return by the way, if i shifted the cold feed from the header tank to the flow would this eliminate pumping to the header tank? - by the way 3 speed circulating pump but its on number 2, tried lowest speed number 1 but still pumps to header tank. and its a bungalow property if that makes any difference.

 

[JohnD]

please photograph the pipe and wiring layout around your pump and valves.

Do you mean that the pump continues to run even when both stats are satisfied and both valves are closed? Why was it wired like that? It probably needs a bypass, or, if there is one, to be opened slightly. Possibly your boiler needs the circulation to run on for a while to cool down.

You will need at least a chemical clean and a system filter to get rid of all the corrosion sediment and sludge. You had better also inspect your radiators to see if they are leaking yet (most likely at the bottom seam)