I thought it might be useful for the Vaillant Arotherm heatpump and its owners to have their own thread. So any questions, queries, things we’ve learnt and performance chatter can go in here. For starters, anyone looking for in depth performance information, this technical document from the Czech …

When were your filters last cleaned? When someone is at home start it up and go into live monitor on the hpui. It will tell you what’s happening. Most likely insufficient flow but if course it could be something else.

Recently by me. And I had the friend check the flow rate and it’s normal. Again today it didn’t run as scheduled, or it started but then stopped, but then resetting on white box and it ran. I’ll check filters when home but Im leaving to software glitch. I’ll probably call vaillant when back as I c…

Hmm Apart from watching Live Monitor.and seeing what it tells you I cant suggest anything else. Note that when you fist go into it it shows -----, wait a few seconds without pressing + or - and it will show status sequentially - I only realised this when my installer showed me!

I’m stumped. Filters clear. Flow rate fine. Again today it didn’t run in the time window or when set to manual. But a reset of white box and it then ran on manual. A few error codes that do not make sense. I think I’ll be calling vaillant tomorrow. F703 sensor fault: low pressure F585 sensor fau…

Have you tried just clearing the faults in the installer menu on the hpai. I have the impression that some faults are fatal until cleared.

@JamesH You said a friend checked the flow rate. Sorry, but why didn’t you check it ? What did the flow rate ACTUALLY say ? What is the spec flow rate for YOUR unit ?

I’ve been away, I had them look when away. And then checked myself again yesterday. It was 1870 l/h and 1050 l/h at 50%. The filter was completely clear as these numbers are my ‘standard’ ones. It’s a 12kw unit. It’s not a flow rate issue.

Im trying to understand the behaviour of my Vailant heat pump in cooling mode. In particular how it decides target flow temperature, and what the 'flow temperature hysterisis means exactly. Here are some plots from today. Its evident that the target FT is increasing during the day, presumably bec…

Vaillant returned today and changed the chip inside the machine again. They said I need to fit a voltage limiter and said they think it was damaged by high or low voltage. The chip they change is the one that stores the machine work life; hours, starts etc. So it’s now back to 0 hours again. A sha…

Vaillant Arotherm Owners Thread

Sustainable Energy

JamesH (James H) 22 June 2026 19:26 1203

Yes. I had cleared the faults before I went away, so these appeared while away. I’ve not cleared them again and we will see. But it smells like the same problem as before. Same codes exactly same issue with failing on DHW run.