Is a Valliant Inline 6kW heater a BUS buster?

GuydeB · 2025-07-15T16:27:03Z

Like many newbies desperately trying to ASHP an old house from oil fired, I have been down many rabbit holes - in brief, three phase not possible (£44K quote from National Grid), 18kW heat loss (Good Energy onsite survey), new ASHP-ready UFH in kitchen extension.One recent suggestion was the (very expensive) Grant VortexAir 15/26kW Oil Boiler and 17kW Heat Pump Hybrid - definitely NOT BUS compliant, but at least a start.However I might have cracked it - or have I?I am considering a Vaillant aroTHERM plus 12kW combined with a Valliant Inline 6kW back-up heater. Looking initially for 45-55 degs flow temp to start (separating the UFH) while we change our rads over the next 12-18 months when finances allow. Plus keeping the existing Joule 300L tank (which we COULD use with just an immersion if ever required).Is this BUS compliant?? We are replacing our old Grant Oil burner - we're rural and not on the gas network (yes we have wood burners but let's not go there!!).Good Energy told me in their opinion this was NOT BUS compliant, my installer said it was but was told by the authorities that until he sends in the documentation they can't tell him (!), Chat GPT is convinced it is as well (!!), but surely I am replacing the fossil fuel with electricity throughout?I'd welcome any thoughts....many thanks this is the inline heater:

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Air Source Heat Pumps (ASHPs)

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GuydeB

(@guydeb)

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Topic starter 11/09/2025 9:46 am

Hi @jamespa and a nod to @grahamf for his excellent old/large house explanations. I am still going around in a vortex of different suggestions without a boiler and struggling to find an installer to help me make the right decision and winter is approaching and my wife is getting nervous!.

A reminder - 1840s 300m2 vicarage - no 3 phase possible - 16.9kW heat loss - new extension with UFH - PHE/bronze pump on the old Joule 300ltr - fam of 4, 2 teens.

My new plan was the 17kW Grant Aerona supplemented by a 4 kW or 7kW Slim Jim electric boiler (dialled down) as a (hopefully) unused back up and try to wrangle the BUS on the basis that it was just that - a back up. Going this route on the basis that no one seems to really know how an old house and an ASHP is going to work until you've tried (!) and for c £550 it seems a good insurance policy (and will reassure my wife).

At this stage we want to stick with the 13 rads we have and change them over time (but also see how the system works effectively bolted on to what's here already - and yes we'll initially need to run at 50/55 degs I'm guessing). Many of the rads are newish cast iron, 4 upstairs are never used and we'll increasingly use the new kitchen extension.

Shoot me down and tell me what I should really be doing!....

The Aerona stats are below: