Secondary return problem

[Gav692]

Had a customer contact me today.
They have brought a property that has an unvented cylinder with a secondary return.
The property has been extended the hot taps in the original side of the house work ok but the hot taps in the extension side run hot for a few seconds then go cold. The run is about 25 meters long.
They don’t know if it’s ever worked ok.
I’m thinking a pump issue, passing mixer or air lock. Anyone else have any other ideas before I go and take a look at it?

 

[snowhead]

My initial thought;
To me that sounds like at first the extension is pulling hot water out the return leg, then continuing to pull cold water out the cylinder, depending exactly where the return is piped into the cylinder.
There should be a non return / check valve on the return at or near the cylinder to stop reverse flow.
This has either failed or isn't there at all.

If you stand at the cylinder with your hand on the return and get someone to open one of the extension taps, if the above is the problem you'll feel the return go from hot to cold.

Another possibiltiy is if the cold is not regulated to the same pressure as the hot and there is crossover at a mixer, probably in the extension otherwise it would affect the original area.

I've had some fun over the years with commercial secondary returns.

 

[Gav692]

thanks for the advice mate I’ll check that first.