CH Expansion Tank. Hot water overflowing

Shovelhead666 · Post by **Shovelhead666** » Wed Jan 10, 2024 2:42 pm

Hi, hope someone can help as I'm pulling my hair out.

I've got a gravity fed central heating system that currently is venting hot water into the central heating expansion tank.

I have used radiator cleaning solution for a week in the system then flushed the system. I have no issue with the circulation.

Also I have two drain off taps at the lowest level with a shut of valve in between the taps. I have used this to ensure when
flushing out the system that both sides of the central heating circuit are flowing properley.
To do this I closed off the shut off valve and opened one drain off taps (LHS). Pumped pressurised water in from the header
tank through the system till good flow and clear water came out of the LHS drain off tap. Once happy with that I then closed
the LHS drain off tap and opened the RHS drain off tap and did the same thing again until I had good flow and clear water.

All radiators are getting warm but still getting hot water overflowing into the header tank.

I do not belive the issue is with the hot water coil as this happens when the hot water is off.

Also the expansion tank does not fill up remains an inch above the central heating feed.

I have 3 circuits one does downstairs the other upstairs and the last one to my expansion tank.
Forgive me if this sounds daft but why wouldn't this type of system not push water to the overflow, gravity ? Is gravity the
only thing stopping this from pumping up to the expansion tank.

Is there a device such as a pressure relief valve that could be used on the overflow feed, could I increase the pipe size to the
overflow 15mm to 22mm to increase the Gravity

Any assistance would be greatly appreciated. Thanks, Jim

Shovelhead666 · Post by **Shovelhead666** » Wed Jan 10, 2024 4:51 pm

I've looked at my system and was wondering if you think the way it is installed may be an issue. ie Pump located on the feed back to the boiler, correct orientation but was wondering if the fact that it is in effect before the expansion tank overflow that might be causing it to push up the overflow pipe.