Expansion tank overflow

[thechauffeur]

Water is coming from my son's overflow pipe on his expansion tank in his loft. I have checked in the loft and found the following. The float valve appears o.k but the expansion pipe that is above it is feeding HOT water into this tank. In addition the water in the tank is filthy and murky.
Can anyone tell me what is causing this and how I could get it fixed. Many thanks.

[The Builder]

I guess this is the expansion tank for the central heating?
Often it's the thermostat on the boiler. The boiler temp then gets too high and overflows.

[alavahalf]

Check your thermostat isn't set too high ...

[AlBags]

IF it is the Central Heating overflow ...

The system is probably over-pumping, that's all. Try turning the pump speed down one click (if you have this setting) or maybe you have too many rads heat satisfied?

Only other option with this is boiler thermostat over-temping .. which needs attention. For this, you can recognise by the noise and bubbles/spouting up to the header tank.

[AlBags]

^ * meant Central Heating Expansion tank (the small one)

[The-HouseHusband]

If the water is very murky it could also be a case of the heating system clogging up. My parents had the same problem which we managed to sort after a couple of applications of flushing agent and draining and refreshing the system.

[tezestwing]

sounds like an old system bit of history would help, the evidence of filthy water leads me to suggest the whole system need a good flush out, if the system was OK before then you should not need to go round altering any settings on pumps etc, that in itself is for the pro,the pump is trying to pump sludge round and the only relief is up the expansion tank,if the boiler thermo had gone it would probably cut out on the over heat any way, but by then it would be making i had better tun you OFF rumble noises
HTH Tez

[geno500]

The pump has been set at to higher speed most central heating pumps have 3 settings nearly all are set at 2,people sometimes put it on 3 because a rad is not heating up and get this overpumping,I would say also the fact that the overflow is in use may mean that there is a blockage in the system,if turning the pump speed does not cure it get a engineer in to clean the system