Why does my central heating constantly vent into the expansion tank?
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Sounds like a power flush job to me. You can make sure of the stat settings, and it could be an airlock in the heating system.
But it sounds like you got a bit of sludge blocking up the system.
You can get some stuff to put in the expansion tank, and leave it in there for how long the instructions say, or go the power flush route, but be careful there are rip off artists out there. The company i work for does it for £350, but if you shop around you may get a cheaper price. There are people out there that charge much more
The tank is buggered, If you look on diy plumbing sites they will mention this.
Could be 'pumping over', the expansion pipe is on the wrong side of the pump, or the pump is facing the wrong way, try reducing the speed as a temporary measure.
water is similar to electric it will find its easiest root to flow. if the heating system is fairly old it may be clogged up in places which will make it easier to travel up the vent rather than around the radiators. also the cold feed and vent connections must be in the right positions so as not to cause pumping over.
check the temperature if it gets to hot it can get to near boiling and will bubble(just like a kettle)and cause air to get into the system,,, check the radiators to make sure they are all getting hot,,
but most of all check the whole system as there may be an air lock causing the water when heating up to vent off,,
the air expands at a far greater rate than water
and will push the water out, and the only exit is through the vent pipe
if and when you have to have a new boiler get a condensing boiler they are better and run cheaper
first thing to try, is to turn down the temperature on the boiler, then try slowing the pump down.
Venting into the expansion tank is a safety feature. But if it is doing it constantly I would guess your thermostat is too high. Mine did it a few years ago and boiled the water in the expansion tank,That caused plastic overflow pipe to melt. Awfull mess had water everywhere. So check that temperature on your thermostat. Turn it down if needed.
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