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Spent £1,000 Trying to Fix My Oversized LG ASHP, Now Considering Vaillant or Ideal. Advice Needed.

Bones · 2026-03-28T20:19:29Z

Hi all, I recently purchased a house in a small development (8 houses) which has an oversized LG 9kw split block fitted, we have had issues all winter and it seems that all of the houses on the development have had similar issues with 2 of them already having had new systems fitted. After spending almost £1000 so far trying to get it sorted we have decided to cut our loses and get a new system installed and I am after some help with figuring out some of the specifics. The house; Built 2017 126sqm Heat loss 3-3.5kW UFH downstairs which is currently set up on 3 zones (kitchen, living room, hall), and 7 radiators upstairs - currently configured so if any of the UFH zones call for heat the radiators will also get heat. When we have had the system working we have had it in WC using the thermostats as a limiter but have had difficulty balancing the upstairs radiators to be comfortable. I have requested the new system to be on 2 zones, downstairs and upstairs (I know that zoning isn't the most efficient but I am willing to sacrifice some efficiency for comfort, ideally I can balance the system and have all zones open on WC mode but having the option to zone upstairs separately would be nice).So the new system we have been recommended is either a Vaillant Arotherm plus 5kw or Ideal logic air 5kw. 210l pre-plumbed cylinder - the installer has recommended a buffer as one of the issues we currently get is a low flow rate, this has occurred less since removing the TRV's but still happens and I assume this is partly down to the unit being oversized. Having read around a lot including this forum I would rather not have a buffer but I am willing to sacrifice some efficiency in order to have a working system - I am going to ask the installer to fit it as a 2-port buffer/volumizer. I should also add that there will be an 18m run of piping that will run 600mm below the garden from the ASHP to the house due to the layout of our house. My question's; - From my understanding the benefit of a buffer is that for much larger buildings you have a separate circulation pump after the buffer - With the run from the ASHP to the house being fairly long, will I need a secondary circulation pump? - If I do need a secondary circulation pump does this mean I have to have a buffer or can you have a secondary pump with a volumizer? - Any recommendations between the Ideal logic vs Vaillant? I know there is a new version of the Vaillant which I would like to wait for but there is a substantial cost difference with the ideal system being almost £2000 cheaper! Thanks in advance

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5016

08/04/2026 6:29 pm

@batpred

You are very welcome.

Daikin 'customer support' was essentially non-existent when I was looking for my heat pump. Basically the answer to any question was 'ask your installer'. I simply don't understand this attitude. Fortunately other manufacturers are available!

This post was modified 2 months ago 4 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.

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Batpred

(@batpred)

Noble Member Member

Joined: 1 year ago

Posts: 1017

09/04/2026 10:32 am

Posted by: @jamespa

↑

If you say a bit more about house size and construction we its possible to ballpark the capacity of heat pump you need, better still if you have records of gas usage.

Our gas consumption (heating, showers, gas hob as electric oven) was:

December 25: 1914 kwh

Jan 26: 2231 kwh

Feb 26: 1667 kwh

Mar 26: 1767 kwh

I described our house insulation before here. We also converted the loft 5 years ago (long story, but we switched to a self managed conversion). But I can confirm the insulation is better than building regs require.

This post was modified 2 months ago by Batpred

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5016

09/04/2026 11:27 am

@batpred ok

My energy delivered in kWh was as follows:

Dec 2777

Jan 3468

Feb 2574

Mar 2390

House is heated to about 21 and it's loss, measured by gas boiler/heat pump, is 7kW. I can rationalise this with surveyed figures by assuming ach=0.5

Unless you don't keep yours warm, your loss is quite a bit less, possibly a match eg to the 5kW Vaillant or if not the 7.

Assuming you do keep the house reasonably warm then if you have detailed records plot daily consumption against average daily outside temperature (or degree days) to get a better indication.

This post was modified 2 months ago 7 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.

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