I have the same, so equally interested in the answer. 

I think its possible that both are correct depending on where they are located in the circuit.  For example a pressure gauge immediately after the water pump will read more than a pressure gauge just before the water pump, the difference being the head required to drive the water through the system

@jeegnesh My heating switched off altogether for three hours today, so the water pump stopped.  Whilst it was off, the water pressure on the controller shot up to equal the analogue gauge at the filler loop.  Once the heating went back on it shot back down again.

So my speculation that both are correct appears to be true, the difference very likely being equal to the pump head, depending on precise placement.

I think that might be an indication of some blockage in the system. I had that difference and lower than the standard vaillant 14 l/min flow rate, until I cleaned the y filter. After I cleaned it the presssure equalised and the flow rate went up. 

God I hope it’s not a blockage already had pump replaced. Also come to think of it the difference was there on Day 0 of install as I remember asking the installers which one is right. 

@jamespa I think maybe you are right, as my pump is also off more often than on now and I’ve noticed during off period it does raise and get close to the analogue gauge, once ASHP goes on the heat pump digital gauge shoots down. 

id have thought while running they would been the same or close not the other way round. 

As I understand it, it depends where the gauges are relative to the pump and blockage. The gauge in the heat pump is before the pump, so where it is lowest, while the one outside for me was before the y strainer. Basically any resistance will drop the pressure, and a strainer with a lot of dirt will drop it a lot. Have a look what components are between the gauge with the high pressure and the heat pump, following the flow direction. It should be one of those components that are causing the problem. 

this assuming the high gauge is on the return flow side, otherwise it’s the whole system and you might have some closed radiator valves or other restrictions. 

The pump off periods I think are due to high outside temp. 
but have a look what the ch pump is set to, it should be on auto. Then check the flow rate, which should be about 14 I think. If the flow rate is high enough, you don’t have much of a problem, except that the pump is probably working harder than is ideal. Mine was an extra 30w when it had to run at 100%. 

Posted by: @adrian

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As I understand it, it depends where the gauges are relative to the pump and blockage.

Agree.  It seems to me that if the external gauge is in the flow, ie immediately after the pump, then it would be expected that there is a pressure difference due to the head needed to push the water through the system.  How much that would be is another matter.

Adrian my knowledge really does not go that far, there are so many pipes in my system, as its mixture of underfloor and rads and lots of everything.  Location of the filler gauge to the ASHP itself which has the digital gauge is significant and I'm sure there a few pipes between them, example pics included.

Just an update, so I had been trying to make contact with my heat geek installer and was getting no response, only to find out they have parted ways, gladly I reached out to heat geek and they are on the case of assigning another heat geek installer to come out and look at the various issues I had been trying to solve with previous installers.  So hopefully we will get to the bottom of this, one thing is for sure the system needs a full flush as my strainer was half covered in crap after 2 weeks of me cleaning it out.

have you got a magnetic cleaner on the system? was it power flushed before install or just warm flushed? also is the analogue gauge upstairs as maybe the height is affecting the relative pressures as im guessing the HP is on the ground level.

re your installer im not surprised, i think some installers have been using the HG label to get work then finding out the HG have chased them when things go wrong at a guess, or the cost of being HG makes things expensive.

looks like a tidy install at least.

Yes there is a magnetic filter (Zeparo) -- I was told it was flushed but I really don't recall a big noisy machine running for hours, so makes me think chemicals or warm flush.

Both gauges are on ground level, in fact I have 3 gauges all ground level, the 2 analogues are identical only the one in the ASHP differs.

when the HP stops and the heating is off do they equalize?