Ground Source Heat Pumps

JHen1

Hi! Any thoughts on why the level in my expansion tank is dropping? When my P3 pump was replaced in Jan 2025 the engineer topped up the expansion tank with glycol to approx 3/4 full - some time after this the level had dropped quite a bit so I topped it up - say 1L approx . I had the unit serviced a few days ago and the engineer mentioned the drop could be caused when the P3 was replaced - air in the system or something - since then I noticed it a dropped a little more. So since I've topped it up after the P3 replaced, its dropped about 1CM - I appreciate this does not help you. It's not a great amount but it does drop - but it doesn't drop daily or even weekly - but it does drop. The engineer said it could be a leak. I have checked the manifold outside and there no obvious leaks. If there was a leak I would expect the level to drop constantly - no ? Should the level in the expansion tank be constant?

beardymarrow

If it's not dropping consistently, I'd guess it's air making its way out of the system and into the tank. As you say if there was a leak you'd expect it to drop all the time that the pump was running, so fairly consistently (weather dependant). Might be worth printing a tape measure and sticking it on to keep track accurately. 

JHen1

I did as you suggested and put some tape and mark on 19/4. Since this it has not dropped, but I know when I last topped it up it did not drop for some time. How would it make its way into the system? The engineer did find the expansion vessel flat and re-pressurised it, but I assume that is not related (the water vessel that is).

lstevensuk

Mine always drops when we have a dry spell, as in last few weeks. I assume it has a leak somewhere and the clay expanding is keeping it closed during wetter times. It maybe looses a whole bottle every year but that's still cheaper currently than replacing whole system.