Can I avoid a bypass

[malcc]

I know why a bypass is normally used for a boiler overrun BUT
I was thinking that I could remove the valve from the central heating so instead of going through the bypass the pump will continue to pump water through the radiators until the boiler is cool enough to shut off the pump.
Reasons
1. Water always flows through the bypass albeit not very much, when the heating is on as the bypass is always open obviously
2. When the timer goes off, the pump continues for quite a long time (varies on how much I open the bypass) and I can manually avoid this by opening up the valve in the heating system (simple electrical stop valve, not a multiport).
The theory is that
a. timer goes off - at same time boiler stops
b. pump continues to pump through heating system until water to boiler is cool enough
c. when boiler is cool enough pump switches off.

It seems a waste of gas to have the bypass running all the time even though it is a small amount, when I could have all the heat going to the rads. By experimentation, I can close the bypass valve balancing the time taken to shut down with the heat lost.
Anyone any thoughts ?
Oh - I realise that when the gas stops, the rads will get cooler quicker as the water will still pump through until the boiler temperature is low enough to shut off the pump.
Cheers

 

[45yearsagasman]

If yours is a gate valve for a bypass, then replace it with an auto bypass, and set it up correctly to only open when system demands it.

 

[sherbert]

what boiler/system have you got
is it 2x 2-port valves or 3-port etc etc

 

[malcc]

There are no hot water/ch multiport. All there is is a two port that shuts off when the CH timer swiches off, at the same time as the boiler. It is this that I want to leave open.
HOWEVER - if I can find an auto that will open up under pressure - that should do the same - it will be closed when the heating in on and will open up when the heating flow stops.
It isn't actually that simple as we also have a flow through the Hot Water that we leave permanently on - theoretically it should close off when the cylinder is hot but I am not convinced. It has a tube attached to the cylinder and a wire that goes to a thermostatic control that is similar to a thermostatic rad valve. The wire does not seem to get hot to the touch as far as I can tell but it is embedded inside the thermostatic valve so the problem with an auto bypass with the current set up is that there may always be a flow through the hot water if this thermostatic valve doesn't work and shut off properly.
I must add that this was not my set up - I would have used a 3 port valve which always allows flow one way or both ways, but I don;t want to have to replumb the whole of the airing cupboard !

 

[Terry lambert]

Plus one for the auto by- pass

 

[malcc]

Ok = seen the DU144 auto bypass. According to Honeywell is is not building regs for these to be fitted - presumably for new sites and it makes a lot of sense.
The 'correct' solution would be to make sure the HW thermostat works and shuts off when the cylinder is hot AND (as suggested - thanks) fit a DU144 (or similar). That way I get the rads keeping warmer longer and it is safe.
Just costs a bit more !