Backflow prevention

[bobcube]

Hi

I had my farm house replumbed three years ago. Every summer, when I turn off the heating, I notice that the radiators still heat up when the boiler hot water circuit is on.

The boiler has motorised valves on the separate h/w and heating feed, but both circuits share a common return.

Having lifted a few floorboards, it seems the plumber connected the returns from various radiators to the common return in at least two places. I suspect hot water from the h/w cylinder circuit is convecting, or being pumped backwards through the radiator circuit (?).

In previous years I've just turned off the rads. Now that oil prices have hit the roof, it's time to properly isolate the HW from the heating circuit.
Is it simply a matter of installing non return valves into the heating return pipes where they join the common return?

Hey - thanks!

Bob

 

[seco services]

have you checked it reverse circulation from the hw return going up the radiator return and not the mot valve letting by ?
reverse circulation can be caused by the radiator return teeing in after the cylinder return.

should be rads-cylinder-boiler not cylinder-rads-boiler.

 

[superdupergasman]

A simple solution to the problem is as you say to fit a non retun valve to the rads concerened but in my experiance this may give bother a few years down the line when you start to get a little dirt in the system.

The best solution is to make the return from the HW cylinder the last conection into the pipework as it returns to the boiler. this will solve all problems.

However in some cases this can be too much work and the former is simpler albeit with a small price to pay when you need to replace non return valves every now and again.

 

[bobcube]

Thanks for the information.

I'm confused. How can the HW return be the last connection?
I effectively have 3 x 22mm pipes from my boiler,

a feed to the HW cylinder
a return from the HW cylinder
a feed to the radiators

The rads are connected into the HW return pipe at various places, obviously after the HW cylinder.

I can't make the HW return pipe the 'last' connection; all I could do would be to connect the various radiator returns into the HW feed pipe!
I may be missing something...?

 

[seco services]

you don't connect the rad returns all the way along the hw return.
connect the rad returns together then to the hw return

 

[superdupergasman]

Cut return pipe from cylinder before first rad return, and then extend HW cylinder return past all the rad connections until the pipe is going to boiler has no more rad return connections then T into that point then you will have rad return pipe and T'd connection from HW cylider.

 

[mickyg]

Sounds like a bodge. Why don't you get the plumber back to sort it????
rad returns should be t'd together into the common before joing the hw return.

 

[ChrisR]

might make things clearer:

Blue + Purplish is flow through the HW cylinder which you want.
Red is flow through the rads, which you don't. The problem is that the red route is in parallel with the purplish one. Though you don't get very much flow, it can be enough to make warm rads.
One solution is often to put a balancing valve on the HW route,. The problem often only occurs when the flow round the blue route is much higher than it needs to be.

One way valves work, but have their problems, and you have to work out exactly where in your system you need one, or more.

 

[liverpoolboy]

on my hot water cylinder it seems like the flow goes into the lower tapping and the return comes out at the higher tapping! it has a pump just after the cold feed (which tees on to the flow from the air separator), the pump is just below this and before the 3 port vale.

the cylinder return tapping (the higher one)!! goes down and the rad return comes up and then the tee together to the common return and go along and down back to the boiler. it looks like it wouldn';t work the way it has been done!