Our First Air-to-Water Heat Pump: Vaillant aroTHERM plus

We’ve just had our first air-to-water heat pump installed, taking advantage of the UK’s Boiler Upgrade Scheme grant. It’s a Vaillant aroTHERM plus, model VWL 35/8.1 A 230V, rated Pmax 3.4 kW, IP X4. That “8.1” in the model code is effectively the generation marker.

The install took 7 working days, with a crew of four: one electrician, one plumber, and two apprentices. It was a lot of work — we also had every radiator in the house replaced, since heat pumps run at lower flow temperatures and need more surface area to shift the same amount of heat.

The outdoor unit sits on a raised bracket against the old stone wall of the house. Single fan, monobloc design — all the refrigerant circuit is sealed inside this box, so only water pipes run into the house rather than refrigerant lines.

Round the back: the R290 (propane) refrigerant label and the red electrical isolator. R290 is a natural refrigerant with a very low global warming potential compared to the older F-gas refrigerants, which is part of why it’s mildly flammable and gets its own hazard sticker.

The flow and return pipes penetrate the wall here, insulated and boxed in with a little metal cage to stop them getting knocked.

Inside, the plant room: a Vaillant hot water cylinder, a couple of expansion vessels, and the manifold where the heat pump’s low-temperature circuit ties into the existing pipework.

Pipe runs across the ceiling, insulated, feeding down to the manifold below.

The sensoCOMFORT controller — flow temperature, room temperature, and system pressure at a glance, with the myVAILLANT connect boxes for remote monitoring mounted alongside.

And the energy display, already logging consumption in Wh. Numbers are tiny so far since it’s only just gone live — worth revisiting once we’ve got a full heating season of data.

First impressions

A few surprises:

• I didn’t expect it to come with an immersion heater as backup for the hot water cylinder.
• It’s so quiet — standing next to the outdoor unit, I can barely hear it running.
• We replaced every radiator, and I’m not sure it was worth it — the new ones are only slightly larger than what we had before.

Next steps

I’ve yet to figure out how to see energy usage from the myVAILLANT app itself. I’m also wondering whether there’s a cloud API I can use to tie this in with our Octopus Intelligent Go tariff — worth digging into once we’ve lived with the system for a while.