radiators getting hot when heating off and hot water on

[xerxesjohn]

Just fitted a Grundfos pump plan (twin headed pump) in place of a three port valve due to constantly sticking. When the central heating is off and the hot water still on the radiators are still getting warm. It would appear to be hot water pump back feeding the central heating system. Flow from the pump is cold on the central heating side when heating off but the return on the central heating is hot when the hot water is on. Does anybody know why? Is it acceptable to fit a non return valve to the return of the central heating to stop this?

Boiler is a Potterton Suprima 100 feeding 20 radiators over four floors
Grundfos twin headed pump

Help!

 

[Jonnie]

pump plans have two single check valves fitted on both out lets, your heating check valve has dirt inside it, this allows the flow of water to creep to the radiators.

 

[xerxesjohn]

thanks johnnie
took pump off and sure enough dirt in both valves now working much better but still getting warm radiators on the first floor above the boiler seems to be gravity (ie hot water will rise) going up the return any ideas

 

[Jonnie]

I've fitted alot of grunfos pump plans and it seems a big problem with them,i've since gone back to fitting "s" and "y" plans because of this. it seems to me that your check valve has still got dirt in it or it is in some way damage , you can get replacement check valves from the internet.the only way the rads can heat up is when the valves are letting by.