One Year Review: Grant 13kW ASHP - A Catalogue of Errors

Air Source Heat Pumps (ASHPs)

Last Post by Mars 17 minutes ago

2 Posts

2 Users

1 Reactions

6 Views

RSS

Solenoid

(@solenoid)

New Member Member

Joined: 12 hours ago

Posts: 1

Topic starter 03/12/2025 9:56 pm

Sorry, this is long (1 year’s ownership).

I bought a new property with a Grant 13kW ASHP installed. It’s been quite the experience so far, sadly. At the time, I was new to heat pumps and didn’t have a clue.

The system failed on move-in day, the coldest day of the year (November 2024), with temperatures between 0 to -1 degrees. We slept in a house with a screaming heat pump and an indoor temperature of 17 degrees, and it stayed like that for days while we tried to heat the house.

Day 1 – Move-in day: The installer (plumber) changed the ASHP controller and heat pump PCB as recommended by Grant Tech Support.

Day 3 – The heating system died. It turns out the cylinder immersion heater kept tripping the RCD. An electrician diagnosed it as faulty, isolated it, and got things working without it. Two weeks later, the installer came and replaced it.

The system continued to fail at heating the rooms, despite our best efforts. It performed terribly at anything below 5 degrees.

Eventually, the coldest days of 2025 (January 10-12) came along, with temperatures dropping to -5. The heat pump stopped producing heat, and the house cooled to 17 to 18.5 degrees (our target was 21), depending on the room. Mid-afternoon I went outside to check if the heat pump was working and saw one slow-moving fan, with icicles on the tip of the other. Icicles were also forming at the bottom of the unit, where it discharges, and there was ice underneath the unit. All the fins were white with solid frost. I figured it was frozen, so I poured two massive watering cans of warm water over the back and side of the unit, which got it going again.

I called a well-regarded (according to reviews) local Grant-registered and trained heating engineer. Here’s what he found:

The system was largely uncommissioned.
The immersion was set to run continuously (leading to eye-wateringly expensive electricity bills from November to February).
The water target was set to 60°C, but the heat pump wouldn’t be able to achieve that target.
All pumps were set to max, even for underfloor heating. He turned that one down to half.
Adjusted the weather compensation from the default (turned up the lower end by 3°C, he said).
Identified that the system was missing a strainer, a flowrate valve, and had zero glycol. I got this all corrected by builder at no extra cost.
The heat pump couldn’t keep up, so it went into a defrost loop? Which caused the cold radiators and underfloor heating (UFH).
The system was never registered with Grant, so no warranty. I got agreement with the builder (who didn’t know), so it wasn’t a disaster.
No documented designs or calculations were available. When I asked the installer for them, they didn’t exist.

I was so shocked by the report that I called Grant and found out the installer was Grant certified and registered. Fun times. There was some bad luck involved, but the installer isn’t a bad guy (really!).

I found this forum 3 weeks ago, and it’s already helped me understand a few things. I’ve made some adjustments and am looking forward to the coming winter with some trepidation. I also called Grant on October 24th for a service and inspection, but I’m still waiting for a call back to book it in. As I said, fun times L

🤔

Quote