Pump stat overun too long

cronley

The plumber made some changes to my central heating. It is an old oil boiler ( non condensing). He fitted 2 motorised valves - one for the rads and one for the hot water cylinder. He fitted a pipe thermostat to turn the pump on and off.
When I turn off the boiler - both motorised valves close down - but the pump keeps pumping for about 2 hours, before it stops. I understand that the idea is to keep the pump going for a while after turning off the boiler, in order to distribute the heat away from the boiler. But with both motorised valves closed down, the pump is pumping against both closed valves, and the heat is staying in the boiler. Is it possible to wire things, so that both valves stay open as long as the pump is going. If this is not possible - I see no point in having the pump thermostat, and my hunch is to remove this stat, and have the pump running only when the boiler is running.
The pump stat is on the flow pipe in the external boiler house, between the boiler and the motorised valve for the rads. The motorised valve for the hot water cylinder is in the hot press on the flow pipe into the cylinder.

K.Flyer

He should have fitted an automatic by-pass on the main circuit.

cronley

Thanks Flyer
Me being a layman - please explain in more detail, the automatic by-pass. Where exactly is it fitted - what does it do - how will it solve my problem.

K.Flyer

Its a valve that opens under the dynamic pressure of the circulation pump and creates an open circuit when the zone valves are closed.
It would be fitted on the main primary circuit so it creates an open circuit when needed.
Why was the pump not wired with the boiler?
Were you having overheating issues on the boiler?

cronley

Thanks Flyer
The motorised valve for the rads is on the flow pipe about 2 feet from the boiler. Is the bypass valve fitted between the boiler and motorised valve, or is it fitted after the motorised valve. How does the bypass valve open the motorised valve when I turn off the boiler.
I dont know if there were overheating issues with the boiler - I doubt it - it is a 1970's bungalow we recently bought. The plumber recommended motorised valves, instead of manual valves.
The pump was not wired with the boiler for the purpose of allowing a pump overun to dissipate the heat.
Are you saying there are 2 options - one is fit a bypass valve - the other is remove the pump stat and wire the pump with the boiler, and have no bypass valve - which would you recommend.

K.Flyer

The valve would go between the pump and any zone valves, it's a spring loaded mechanism which does not interact with the zone valves.
If there were no previous overheating issues when the boiler shut down, I would have the pump linked to the boiler and both activated by the aux (orange and grey wires) from the zone valves.

cronley

Thanks Flyer
I will go with that. I will get the plumber/electrician to remove the pipe stat that governs the pump, and wire the pump with the boiler, so that the pump turns off when I turn off the boiler, and there will be no pump overrun.