Circulation pump conundrum

[Gavwatson]

i have a regular Worcester boiler heating water in a thermal store via a short closed loop with a copper coil in the thermal store. The water in the thermal store is pumped round the central heating and the store also provides domestic hot water via a heat exchanger. The water is also heated vía a back boiler on a log burner. The thermal store thermostat is set to around 80 degrees as recommended by the manufacturer. However before the water reaches this temperature the boiler turns itself off but the pump that pushes water from the boiler to the store through the coil keeps running. This pump never goes off and runs 24/7. So water is constantly being pumped through the coil in the thermal store.
Any ideas what’s going on

Also I’m thinking of upgrading the boiler as it broken at the moment. I have a 4 bed detached house with 11 radiator. What kw output boiler would be able to easily deal with this. Was thinks of Worcester 4Ocdi regular boiler but not sure if this is too much

Thanks

 

[Chuck]

Any ideas what’s going on

Site unseen, my guess is as follows:

To transfer heat to a thermal store at 80°C the boiler flow temperature will need to be between 85-90°C. Most domestic boilers have a maximum flow temperature of ca 85° and the burners will cut out above that but, because the store is still calling for heat, the pump will keep circulating. Also the arrangement you describe will have a high return temperature, which might also cause the boiler to cut the burners.

Combining a gas boiler with a back-boiler and/or a thermal store needs to be done right. Get a heating engineer to review the settings and controls for you.

 

[Gavwatson]

Site unseen, my guess is as follows:

To transfer heat to a thermal store at 80°C the boiler flow temperature will need to be between 85-90°C. Most domestic boilers have a maximum flow temperature of ca 85° and the burners will cut out above that but, because the store is still calling for heat, the pump will keep circulating. Also the arrangement you describe will have a high return temperature, which might also cause the boiler to cut the burners.

Combining a gas boiler with a back-boiler and/or a thermal store needs to be done right. Get a heating engineer to review the settings and controls for you.

Thanks very much for the info. Appreciate it