Obviously it is difficult to give a definitive answer without carrying out detailed testing, but here are a few possible ideas.

The water pressure mentioned will be the water within the heating system, which is a sealed system that should have a pressure of around 1 bar to 2 bar. It is not the mains water supply pressure.

The fact that you are getting several sensor faults together would make me suspect a circuit board problem or a data communication problem, or even something as simple as the incorrect version of firmware.

First thing to check. Do any of the data/communication cables run next to, or near to power cables? This could lead to corruption of the data signal being passed between the different units.

An 'dry joint' or bad connection on one of the circuit boards could also cause the system to fail to operate correctly. Have any of the circuit boards been swapped for known good ones to see if this cures the problem.

Has anyone checked the installed firmware version to confirm that it is correct?

@derek-m Thank you for the answer, appreciate your time. 

At various times, faults such as you describe have been suggested by the engineers. All discrete circuit boards have actually been replaced due to faults, in some cases more than once, the wiring has been replaced to eliminate the interference issue as a possibility, and several loose components have been reseated/resoldered. All sensors have been replaced too.

I think it might just be a bad unit, a lemon if you like. I haven't checked the firmware version but will make sure that is up to date. Had to restart the unit 14 times yesterday, 8 times today! 

Chief engineer is here on Monday at last, so will see what he has to say. I'm intrigued by the anticycle time as I can't for the life of me think why that value would ever need to be so high. Obviously it has no upper limit imposed in the software, but some kind of input or calculation must be going awry for it to reach that number. 

I'll update when the engineer has been, can't hurt to post the info in case someone else experiences a similar situation.

Thanks again! 

Hi there, I'm very curious if you got this resolved?  I have a new Vaillant Arotherm Plus that is exhibiting the exact same problem (multiple faults, very high anti-cycle time).  Did you get to the bottom of it?

@cg360 can you please provide us with an update?

@editor In the end a Vaillant engineer came out and was a bit mystified, but replaced the main PCB in the front top right corner of the unit.  Since then the problem has not recurred so hopefully was just a defective board.

The ASHP has been working perfectly for a number of weeks now but just today failed with another issue F1117 "Compressor Phase Failure"... so back to Vaillant for assistance again!

@dant7 wow, what a pain? So I assume your heating has gone off completely on the back of this fault, correct?

@editor Yes it is indeed out of action.  Luckily the cold weather hasn't really started yet and the engineer is booked in for Thursday so hopefully will be resolved quickly.  I did a bit of testing - the board at the back is getting power and no obvious damage.  Tech support said it could be a fuse or other failure elsewhere in the unit - the engineer will investigate.

I’m sorry - I thought I had replied but I don’t see it!

Eventually my HP unit was replaced after the senior tech engineer came out to do a deep dive.

He could find no faults and replaced some components but to no avail. Unit failed two days later. 

Have had zero problems since replacement and I would add that while we were OK with the performance of the original unit when it worked, the new one is light years ahead in speed of heating hot water and firing up the heating. So the original really wasn’t ever performing up to the expected standard. Odd to think they couldn’t figure that out, but there we go. We had nothing to compare it to because we had a combi gas system before and were expecting some compromises.

The old unit went to a local college for training purposes.

@cg360 Hi thanks for replying - unfortunately my unit is now showing the same issue as before.  Multiple sensor faults and massive anti-cycle times.  I have a vaillant engineer coming tomorrow - is there any reference you have for your case I could refer them to?  It may lead to a speedier resolution!

If you could contact me off the forum my email is dan_tomlinson77@yahoo.co.uk

Hi all, the issue has been resolved (fingers crossed) for me.  It took two Vaillant engineer visits - they replaced the control board on the front right of the unit on the first visit but that didn't work.  On the second visit, the engineer was a bit stumped but ended up replacing the rear power board and the entire wiring harness.  That did the trick and it has been running reliably for the last month or so!