Pump overrun with multizone system

[Snowman1]

I have a central heating system with 3 heating zones and hot water. Is there any way to to use pump overrun properly so that the last zone satisfied does not close the motorised valve until the pump overun switches off. Otherwise I either have to disable it ot let it run through the bypass - both of which are wasteful.
Many Thanks

 

[Roger Welton]

Whilst I'm sure it is possible, via several relays, common practice is to run it though the bypass.

 

[chris watkins]

Only way I can think is to re-wire system so that one or all of the htg zones are open unless hot water is on (priority hot water) but this would only be worth while doing if you are going to do other things like fitting one to the new pumps which will not work with an auto bypass.

 

[Snowman1]

Thanks for the replies. Whereas I can see the easy way out is to use the bypass, that does seem wasteful.
To try Chris's thought, I guess I would need a relay driven by the "call for heat" signal to the boiler and select one zone and connect it to a NC connection on the relay or can you thing of a better way?
That is at least using the hot water in the system albeit going into a zone which, unless it has just been on, will have cold water in it! but I can't think of an easy way to make that pick the "last satisfied" zone. I suppose that is beyond the scope of a couple of relays!

 

[Mike Jackson]

Put a bypass rad in, perhaps a towel warmer.

 

[AWheating]

normally open zone valve. or zone valve wired to pump overun? would need some thought tho.

 

[Roger Welton]

Put a bypass rad in, perhaps a towel warmer.

This is what I have at home

 

[Nostrum]

How much money will you save, compared to the cost of modifying the system?

You'd be better off leaving it as is if you ask me. It's unlikely all zones will be satisfied at the same time for long enough to waste any relevant amount of heat, you'de be better off lagging the pipes up to the bypass.

 

[Snowman1]

I suspect that putting my towell warmer on a continuous zone rather than a controlled one will be the best answer as probably having a zone valve open always will cause premature failure in the motor which will negate any possible savings!

 

[DirksPlumbing]

How about using a three port valve?