Intermittent hot water on Heatstore

[Class of '55]

Hi, I have a Gledhill 2000 Heatstore. The hot water intermittently runs hot and cold. 1st port of call and the pump’s ‘humming’ when being called for. Found the pump free when checked at the spindle. Reading up some have suggested the dhw sensor but I wondered if that is likely considering the pump seems free. I obviously need to consider more but these aren’t my strong point and would welcome your views before I go blundering in.
Can you suggest a rplcmnt pump for the Fos 15-50 as they seem obsolete. I’m assuming it’s a bronze pump

Any help greatly appreciated

Steve, retired Gas engineer.

 

[Dangee]

First port of call is to check the blending valve. When the water goes cold, fell the hot connection to the blending valve. If it's hot, it's the valve. Common issue.

 

[Dangee]

Also, whatever happens you won't need a bronze pump. Check the pump actually spins when called for. All that that pump does is circulate water through a heat exchanger when there is hot water demand.

 

[Class of '55]

Thanks Dangee, I’ll check that out.