System pressure drop when heating is oon

[spacebiscuit]

Due to some recent building works the hot water cylinder that was in my. loft was relocated and some legs have been run for 3 more radiators which have yet to be fitted.

Hot water has been fine since the relocation of the cylinder around 4 weeks ago. This weeknd I put the heating on, all was fine but next morning when the hot water cycle ran (before the heating comes on).

The hot water and heating is supplied via an air source heat pump, the unit showed a low pressure error so I filled the system to about 1.7bar when heating was on and bled the radiators. I manually put water cycle on and cylinder had hot water.

Next morning after heating had been on the night before same problem. It seems that when I fill the system within about 30 mins pressure drops to 1 bar or less, however all rads are nice and hot.

Seems the pump itself is fine but something within the system needs adjusting. I should also add that a new expansion vessel was fitted to the cylinder when it was relocated.

Any ideas? Thanks.

 

[Wayners]

Cracked heat exchanger maybe.
Water evaporation inside so nio sign of leak

 

[spacebiscuit]

The hot water cycle had been functioning fine, the pressure drop has only occurred since the heating has come on. If it was the heat exchange the pressure drop issue would have occurred before the recent period when I put the heating on....

 

[spacebiscuit]

I found the water is escaping via the over-flow pipe that runs from the expansion vessel pressure relief valve. The plumber replaced the vessel but I don't think he changed the valve. As soon I try to fill the system the water pours out of the pipe that runs through the external wall to the outside.

 

[Madrab]

Yep - Sounds like PRV is letting by. That should all have been tested by your 'plumber'

Does the wet side of the ASHP just use water - some use specific additives/ etc so especially for winter protection, has the ASHP installer/manufacturer OK'd just adding water to the system?

 

[dilalio]

Crank the red cap on the prv a few times and see if it re-seats.

 

[spacebiscuit]

Yep so the PRV was knackered it seems, I have added a new kit and now the pressure is stable and system is not losing water.

Any recommendation for additives that I should add to the system as it was drained down several times and I've lost a lot of the good stuff i guess.....

 

[Madrab]

System size dependent then get at least a bottle of inhibitor into it. Buy the well known makes - Sentinel/Fernox/Scalemaster etc don't buy budget.