2 x 2 port valves

[Sandy43]

If I have 2 x 2 port valves, means one for heating and other for hot water,
must I have a by pass valve? otherwise when both heating and hot water
valves as shut, there will not be any path for the water to flow. This pumped water then should flow through the by pass valve that should be open fully at this stage.

Should the signal that switch the boiler off should also switch the pump off
as well rather than through the boiler as a "run over". In this case it will
not switch off the pump till the heat exchange cool down to certain temperature?

 

[gas4you]

This all depends on which boiler you have, or intend to have.

If the boiler has a pump over run built into it, then the pump needs to be wired back to the boiler and an auto bypass fitted for when both valves are shut.

Some modern boilers have a built in auto bypass that is man enough to do the job without an external one being fitted.

 

[Sandy43]

Dave thanks for your helpful answer. It does enhance my knowledge and help me to decide what to do in my present project.