CH/Hot water pump runring continuously

wizzer

Hi,
Recently had new energy efficient boiler installed plus accessories plus some new pipework etc (eg ancient floor standing boiler under stair cupboard moved to wall in utility room). I've noticed that the pump seems to be running constantly even when the boiler is not alight. So for example, if the timer brings the HW on at 7.00am and turns it off at 10.00am then the pump is running throughout this period even if the hot water has reached its required temperature by the cylinder thermostat.

This doesn't seem right to me. Can anyone advise?

Thanks

Ted_Hutchinson

Generally the cylinder thermostat should only call for the pump to be on if needed. Are you sure the pump isn't also serving the radiators?
Diagram of typical system here

wizzer

Yes, I presume the pump does serve the radiators as well but these are off at the moment (off at the wall thermostat) because of the mild temperatures at the moment.

Thanks

fifeken

The pump will be for the central heating, I think, and will circulate water through the system even if the radiator thermostats are turned down. This is so that hot water is available to any individual radiator that requires it. If you don't require any of the radiators to be on then the control panel should allow you to select HW only and no CH. The pump should then go off.

paul_h

If the pump runs when the boiler is not fired up, then it is wired up incorrectly. The timer/thermostat output to the boiler should also be connected to the pump, so they both run together when calling for heating.

wizzer

fifeken wrote:

The pump will be for the central heating, I think, and will circulate water through the system even if the radiator thermostats are turned down. This is so that hot water is available to any individual radiator that requires it. If you don't require any of the radiators to be on then the control panel should allow you to select HW only and no CH. The pump should then go off.

No the pump runs even when the CH is switched off.

Ted_Hutchinson

If the central heating is off and the cylinder is up to temperature then there is no reason why the pump is still running. So it must be wired up incorrectly.
If you look at the diagram and imagine that both the valve to the hot water cylinder and the valve to the radiators are closed where is the pump pumping water too?
if all the possible outlets are closed it's wasting energy, costing you money and wearing itself out for nothing, pumping water against closed valves.

alanobrien

wizzer wrote:

Hi,
Recently had new energy efficient boiler installed plus accessories plus some new pipework etc (eg ancient floor standing boiler under stair cupboard moved to wall in utility room). I've noticed that the pump seems to be running constantly even when the boiler is not alight. So for example, if the timer brings the HW on at 7.00am and turns it off at 10.00am then the pump is running throughout this period even if the hot water has reached its required temperature by the cylinder thermostat.

This doesn't seem right to me. Can anyone advise?

Thanks

The pump can / will continue to run for a while once the heating has been on. This is so that the system can cool down efficiently.

Could be the boiler thermostat is set to high, this is usually a simple dial on the boiler.

Alternatively, there is also something called pump overun explained quite nicely here

http://www.tertullian.org/rpearse/heating/overrun.htm

that can occur if you have a duff thermostat on the boiler.

paul_h

The problem described by alanobrien sounds feasible, although these pump overrun devices are not fitted to all boilers.

One thing that bothers me though, your original post states that the pump stops after the timer goes off, I'm pretty sure these overrun devices continue to operate after the timer/thermostat switches off?

The boiler has a permanent supply to enable this to work...

It still sounds to me like the pump is connected to the timer output to the thermostat, rather than to the thermostat output, as your boiler is..

wizzer

paul_h wrote:

One thing that bothers me though, your original post states that the pump stops after the timer goes off, I'm pretty sure these overrun devices continue to operate after the timer/thermostat switches off?

The boiler has a permanent supply to enable this to work...

QUOTE]

Have spoken to installer who has said maybe he's wired the pump incorrectly so he's coming back to take a look. Sorry to clarify, yes there is a slight overrun when the programme turns off.