Wiring for dual circuit and pump overun?

[AndyTh]

Hi all. First post - be gentle.

I have added major extension to existing house. There are two pumps each supplying a separate CH and HW zone valves. The boiler is a Worchester CDi conventional. The boiler has an overun circuit that keeps the pumps runing for 3 min after the Heating demand stops.

My problem is that when the programmer or stat stops, all the valves close while the pump keeps running for 3 mins. Pump is deadheading and there is no flow through boiler.
How should the pump be wired?

Note that there are two in fact two pumps, how would I control these separately, both for normal operation and during boiler overrun.

Appreciate any help. Cheers
Tried to insert Picture of circuit here, but rejected. How can I share a picture?

 

[AndyTh]

Found insert image but this is all I get.
I am on ipad and trying to load from photos. What am I doing wrong?
[MENTION] [/MENTION]

 

[kozak1968]

You need an automatic bypass valve to be fitted after the pump and before the 2 port valve. This will allow a flow through the boiler when the call for heat is off which will protect the heat exchanger.

 

[AndyTh]

maybe picture worked now?

 

[kozak1968]

Do you have a pipework drawing. It sounds like its more to do with the pipework configuration than wiring.

 

[AndyTh]

I see I have managed to post picture twice, but upside down. This should show that I have in total 4 single valves and two pumps.

Kosak - thanks for reply. Not sure how that would work and it brings up another problem. See my other post on expansion pipe and pump over. Is there not an electrical way to solve the problem?

 

[GasmanxxxR1]

You will need an auto bypass, the pipework should never have been put in without one

 

[jtsplumbing]

Why 2 pumps ??

 

[ShaunCorbs]

Why 2 pumps ??

one for heating and one for hot water (heating system must be big)

or a back up for the first one

 

[jtsplumbing]

Would be useful if he told us what size system he is running !