Posted by: @get

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Hi, thanks for the reply. The air is from the domestic hot water cylinder that is contained inside the heat pump. 

OK.  You dont say whether it is from the feeds to/from the DHW cylinder carrying hot liquid from the heat pump, or from the cylinder itself.  Either way its a simple plumbing issue.

If its from the hot tank itself then most likely something is wrong with either the input valves (normally a pressure reducing valve and a pressure relief valve) or the (normally white) expansion vessel, or alternatively your mains pressure has dropped to below the level set by the pressure reducing valve.  This is regular plumbing and any plumber used to UVCs should be able to sort it out.  

If its from the feeds to the hot tank then it depends on whether, in your heat pump, these are somehow separate from or connected to the system that feeds the space heating.  If the latter (most likely) then the system needs a top up or the expansion vessel (normally red) needs repressurising.  Again nothing that any plumber used to central heating systems of all types shouldn't be able to sort out. 

If the hot feeds to the tank are somehow separate from the hot feed to the space heating (or even refrigerant not water, which is just possible) then its a bit more heat pump specific and you may need someone familiar with heat pumps and preferably ground source heat pumps.  The installer who put my ashp in also does repairs for GSHPs so Im guessing that at least some other installers do similar, the basic components are little different so someone with a bit of intelligence who can read should be able to work it out (I realise that excludes some installers, sadly).

Hope that helps, the manual might point you in the right direction to distinguish between the cases above if you dont already know.

Posted by: @tdudgeon

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I have an IVT Greenline HT Plus C heat pump that is continually having errors when heating the hot water cylinder.

Both “Electrical cassette” and “High pressure switch” errors are happening several times a day. Acknowledging the error lets the heat pump continue, but clearly something is wrong. Previously I had problems with “High HTF Delta” that seemed to be this problem, which seemed to be fixed by changing the pipes.

Any thoughts on what needs to be done?

Can you post pics of the cassette and heat pump set up, pipe work between them if possible? High pressure trips, assuming temp sensors and pressure sensors are reading correctly are pretty much always flow related. Is there a strainer in line with the hot water tank? Is the tank heating as quickly as it used to? If you start up your rads, does the system run normally?