Secondary return cools cylinder within 2 hours

[oz-plumber]

I would hazard a guess that there is something else going on when the secondary return pump is on.
I doubt you would lose the heat from the cylinder and pipe work in that amount of time, if you haven't used any hot water.

Is there a pressure relief valve on the secondary circuit that may be passing when the pump is running?
This would cause an influx of cold water to the system - when the pump is running.

Sounds odd, but even un-insulated pipework, should not lose that much heat over that time.

 

[Peterdevon]

I had the same problem, the pipework under the ground floor was uninsulated and would cool the cylinder in about 2 hours, I have now got 19mm lagging on all the pipe work but it will still go cold if the pump is left running all day.

 

[Ben Adams]

What size pipework has your hot pipework and secondary return been ran in?

Hi Simon, thanks for the response. I've just been up in the loft and it looks like the hot pipework has all been run in 22mm pipe with the secondary return in 15mm. Thanks. Steve

 

[Ben Adams]

I had the same problem, the pipework under the ground floor was uninsulated and would cool the cylinder in about 2 hours, I have now got 19mm lagging on all the pipe work but it will still go cold if the pump is left running all day.

Thank Peter, that's interesting to know. Hopefully insulating the pipework in the loft will help! Thanks

 

[Ric2013]

Well, I'm thinking if your HOT OUT goes in a roughly upwards direction from the cylinder, you may be getting one-pipe circulation within that pipe even when pumps are off and no one is drawing water. From the photos, I'm having a hard time visualising which way is up and what connects to what, but if you follow the pipes with your hands, you'll soon get the idea which pipes are getting hot (losing lots of heat!), and which pipes are merely getting warm.

Last time I looked, Toolstation had some pretty good prices on what they call 'byelaw' insulation. It's only 1m lengths, but if you evostik all along the split and joints, it should work well.