Sudden pressure loss in ASHP system

[kandgmitchell]

Hi,

I've a Vaillant Arotherm heat pump system that's been in and working for about 18 months. During that time we have experienced 3 cases of total loss of pressure in the system. The last was whilst we were away abroad last week and I had to talk my daughter through topping up the system using the filling loop, and re-setting the pump- isn't WhatsApp wonderful!

 

There is no water in the tundish and the loss is sudden not a gradual creep. This suggests there isn't a leak in a loop because one would expect the pressure to degrade over time. It's almost as if the system is initiating an irregular process that involves using a particular valve or suchlike which when used, dumps the pressure and causes the system to shut down.

 

I am about to start the process of taking this up with the installer but thought I would put the problem out there so I can approach them with a bit more knowledge.

[SimonD]

Have you checked the anti-freeze valves? Big puddle of water around them?

[JohnMo]

So was system off while away, or running normally?

 

What is your normal system pressure?

[Nickfromwales]

Any particular time of year for each ‘event’?  

[sharpener]

22 hours ago, kandgmitchell said:

I had to talk my daughter through topping up the system using the filling loop, and re-setting the pump- isn't WhatsApp wonderful!

 

I wonder does it just let the pressure down to zero, or does it dump a substantial quantity of water beyond that and so need a lot to refill? Might be a clue in how much air you have to let out afterwards. 

A pressure relief valve when tripped might not re-set and continue to let by. There have been quite a few reports of the PRVs in the outdoor unit being faulty and replaced under warranty, you might not notice that as IIRC the outlet goes into the condensate tray and thence to yr soakaway, that is where I would start looking.

 

22 hours ago, kandgmitchell said:

It's almost as if the system is initiating an irregular process that involves using a particular valve or suchlike which when used, dumps the pressure and causes the system to shut down.

 

 

Unlikely IMO, in that even if your system is divided into circuits the return pipework will go to a common point so everything will be at the same static pressure irrespective of which valves are open.

 

 

Edited 5 hours ago by sharpener

[kandgmitchell]

In all cases the system was up and running normally, the last two events were 27th October and 18th November so about 3 weeks apart, the first was back in the summer. Whatever is releasing the pressure must re-set itself as you can top up and get everything working again. Currently working normally since the 18th. No obvious water anywhere. It doesn't take much filling from the loop to get the pressure back up.

 

 I've got a horrible feeling this is going to be like one of those odd noises in a car that the mechanic can never find.....