DIY Doctor UK DIY Forums

Hi
Can anyone help? The radiators get hot at the top of the house when heating is off and hot water is on.
I do not have a 3 way valve, apparantly a v old system. My pump which was suspected has been replaced

The thing about hot water is, that it is less dense than cold.....therefore it tends to rise.

Gravity circulation it was called in my day......I think they call it thermosyphon these days.....

I've installed entire heating systems working on this principle some years ago......no pump needed.

Anyway.......all you need to do to stop it, is to fit a check valve or non return valve after the pump.

Thanks I will speak to my plumber

Thanks Jon,

The plumber is coming out and thinks your suggestion will fix the problem.

One further question. The system has been ok since we moved in five years ago. A year agonoticed one of the rads getting hot at the top of the house and susspected a (non existant) 3 way valve. Then recently gets worse rads on floors one and two getting hot. Would thier have been a non return valve built into the old pump (which failed) cause it's a recent problem?

Hi,

I had this issue until recently. Whenever I turned on just the hot water, the rads would heat up. This was due to reversed circulation which occured because the radiator returns joined the return pipe after the pump/cylinder in 2 places. The radiator returns should all common up into one pipe then connect to the return after the cylinder. Rad returns joining at more than one point affects the flow pressure and allows water returning to the boiler to flow into some or all of the radiators via their returns. Check your radiators return pipe when turning on the hot water to see whether it heats up before the feed.

Hopefully I have explained this well enough!

maybe a plumber can explain it a little better than I.

Hi jamie.

You are quite right, all heating returns should be joined together before they reconnect to the primary return, however Chard said it has been working ok for five years so I discounted any pipework problems.


What is a surprise is why it should suddenly start to happen, I do not know of any domestic pump that has a built in check valve, though it is possible that a check valve was fitted very close to the old pump and it was removed along with that.

I must admit, not being able to see the system pipework does make it very difficult to give a precise diagnosis.

Thanks Guys,

New check valve installed & all seems OK it will (probably) remain a mystery.

Chard