Pump is running dry?

[dr__red]

We’ve got 2-inlets/2-outlets/single speed dial pump installed next to HWC in the airing cupboard. It is gravity fed, i.e. with cold water tank in the loft. The pump boosts en-suite shower and a bath tub.

From time to time when running the bath the pump switches into high revs and cold water drops pressure considerably, often stops. It is never an issue with hot water. This makes me think cold water tank must be running out of water ? Is it likely? When this happens it also takes a while for bathroom’s flashed toilet to refill - I hear how air bubbles struggle through the pipes before we get a flow...

Still I have a hard time to believe into dry tank scenario... I usually let it “rest” for a while, then run cold water with the pump being switched off – this seems to “cure” the issue.
What do you think is a likely cause of the failure and how to rectify?

 

[gas4you]

Certainly sounds as though the cold tank is running dry from what you have said. If you can't believe it why not go into your loft and check it next time it happens

 

[dr__red]

yeah, it also crossed my mind, unfortunately this usually happens when I'm in the bath or about to get into one. Not exactly in climb-to-the-loft-with-a-torch mood. But I'll take it as a sportsman next time...

 

[dom2466]

Dr Red, did you go up into the loft with your bathroom on and see if it was the cold water storage cistern that had run dry ??