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[Solved] Vaillant aroTherm not heating with many faults

Anon67 · 2026-01-10T21:01:29Z

I have a 3 year old 10kW vaillant aroTherm heat pump connected to dhw and ufh. The heat pump kicks in on demand for hot water but when it comes to heating it faults, getting a mixture of faults F.732 Compressor outlet temperature too high F. 733 Evaporation temperature too low F. 0521 Outdoor temperature sensor signal invalid Does anyone have any ideas how I can get the heating back on even temporary? Until I can get someone to look at it on Monday. I tried looking through the menu but there doesn't seem to be any option to force heat.

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Air Source Heat Pumps (ASHPs)

Last Post by Majordennisbloodnok 9 months ago

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Anon67

(@anon67)

Active Member Member

Joined: 9 months ago

Posts: 6

Topic starter 16/01/2026 11:59 am

Thank you all for your help with trying to get this sorted. Just a quick update to close this thread off incase anyone has similar in the future.

I phoned Vaillant on Monday, spoke to the tech support line, he said going off the fault codes he suspected it to be low on refrigerant so he booked me an engineer visit.

Tuesday morning the DHW started faulting displaying similar messages compressor blocked etc

Guy came out late yesterday afternoon, zero pressure in the refrigerant circuit, pressured it up with his test gas, could watch pressure dropping off immediately and could physically hear a leak. Traced to the evaporator, which isn't replaceable or repairable so they are replacing the full unit.

Hopefully it'll be all sorted by next week.

This post was modified 9 months ago by Anon67

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ASHP-BOBBA

(@ashp-bobba)

Prominent Member Member Professional+

Joined: 2 years ago

Posts: 501

16/01/2026 12:04 pm

@anon67 Pleased they are replacing it for you and I am pleased when I said they are quite good with their warranty they actioned it.

Good luck with the replacement

AAC Group Ltd covering the Kent Area for design, supply and installation of ASHP systems, service and maintenance, diagnostics and repairs.

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Mars

(@editor)

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Joined: 6 years ago

Posts: 4918

16/01/2026 11:24 pm

@anon67, glad to hear they’ve found the issue and that it’ll be replaced. Hopefully that goes smoothly. Will Vaillant be doing the replacing themselves?

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Majordennisbloodnok

(@majordennisbloodnok)

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17/01/2026 1:05 pm

The mark of a good company to deal with is less to do with them not having issues as much as how they deal with them when they arise. Glad you’re on the way to a quick resolution and props to Vaillant so far for playing fair.

105 m2 bungalow in South East England
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