Cold feed is hot even after powerflush

[dominoman]

On my open vented y plan central heating system the cold feed pipe that goes up into the F&E tank gets really hot. The expansion pipe (larger 22mm diameter one) doesn't.

Does this indicate a problem?

 

[Gasguru]

No, as the water is heated it expands in volume and flows back up the expansion pipe to the cistern.

 

[dominoman]

No, as the water is heated it expands in volume and flows back up the expansion pipe to the cistern.

In my system that expansion pipe doesn't get hot at all though, and the cold water feed is the one that gets really hot.

 

[ChrisR]

You have two pipes.
One is Feed and Expansion, the other is VENT.
Expansion water goes into the water tank the same way it came out. The vent is a column of water which only goes up and down an inch or so.

It/they both get hot through convection, unless you take steps to prevent it.
They both have a level change when the pump stops & starts, quite a kick if there's any air in the system at all. You will have some air for a few days after a PF. Bubbles inthe water.

So you can insulate if you like, but otherwise don't worry unless there's air being sucked into the vent (try holding a cup of water to it) or water coming out of the vent.

 

[dominoman]

Many thanks. That helps a lot.

Yesterday after the power flush there was water coming out of the vent when the pump stopped. We only discovered this as the vent wasn't quite over the F&E tank so ended up on the loft floor.

Hopefully that is just because there is still air in the system and it will soon settle down.

 

[ChrisR]

Yep, pretty normal, for a few days sometimes. The trapped air acts like a spring so when the pump stops and it's no longer compressed it pushes back.

If it won't quite stop, you could take the loop (inverted U) of the vent pipe a bit higher. You don't want it circulating, because that takes oxygenated water fom the tank down into the system, which eventually leads to needing another powerflush ..