Grant ASHP 17.5 kw. weather curve

Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 37 minutes ago

2 Posts

2 Users

0 Reactions

12 Views

RSS

Chinkoa

(@chinkoa)

New Member Member

Joined: 6 hours ago

Posts: 1

Topic starter 01/01/2026 6:04 pm

I have had my Grant ashp and radioators installed for about 18 months ago by a company whos premises are 200 miles away. their handover consisted of, i've left it running don't touch any of the settings.

Well winter came and the ashp kicked in. we had to run fan heaters to keep warm. several of the radiators were stone cold. A year later i had it serviced by Grants the makers. he very kindly retune it for us, the installer set the weather curve setting to off? any how by and large the system is working pretty well when the outside temperature is 2c upwards. But now the winter has kicked in an the temperature has dropped. just now -5c when i looked at the settings on the standard controller the parameter 2104 is set at 0 radiator temperatures are at 31 c. All trv are fully open and stat is set to 25 deg bur us showing 18c. W e live on the North coast of Scotland in view of the North Atlantic. my settings are:-

2100 1

2102 45

2103 35

2104 0

2105 20

What do i need to set the wc 2104 to?

Quote

Topic Tags

weather compensation sett

JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 3779

01/01/2026 10:04 pm

Firstly welcome to the forums.

I hope you are running your heat pump 24*7 with any TRVs and thermostats set well above the desired temperature so they have no effect other than when there is excess solar gain. Assuming we are over that hurdle then:

With 2104 set to 0 the FT (and therefore your emitter output) will flatline at 0. However your house demand will keep increasing as the outside temperature falls so inevitably the house will cool because the output of the emitters depends on flow temperature so, even if the heat pump can generate more heat, the emitters cant transfer it to the house.

Its impossible to be prescriptive on temperatures because it depends entirely on your house but 2104 needs to be set to (or below) the minimum OAT at which you want the heat pump to heat the house and 2102 adjusted accordingly. I dont know how cold it gets where you are, but if you were say to set 2102 initially to 50 and 2104 to -10 this would give the same curve at OAT above 0 but extend it when OAT falls below zero. Based on your statement that it works well at OAT>2 this shouldn't be far out. You can then tweak 2102 up/down (slowly, no more than one degree per day) to get it exactly right.

When it is mild expect radiators to feel cool at most, 35 doesn't feel hot to the touch! If however they are stone cold (and assuming no active TRVs) then you may need either to bleed one or more of them or balance them.

This post was modified 34 minutes ago by JamesPa

This post was modified 33 minutes ago 2 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

ReplyQuote