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Hi all, I currently have two Willis heaters (Read more here) providing the 6kW for the slab (proving very expensive now), I am now looking to get an ASHP installed. Question is, should I go via the BUS grant or should I source a unit off ebay and either attempt a self install or get a local fitter to install? I'd like to think that the grant would now cover the simple install! Further questions: How long does it take once the installer has applied for the £7.5k voucher? I'd like to have an install completed ASAP before the temps drop and there's a significant demand for heating in the house. The setup would be fairly straight-forward, with the heat just being fed directly into the slab, so no need for cylinder etc. Previously (2019) I had a quote for a Mitsubushi 8.5kW which also included the installation only of 2 Sunamp units (previously purchased but now installed) which came to £8,000. Presume that would have been a 2 day install at max, so imagine that realistically, today's figure would be less! I expect of course to get a much inflated price back when I go back for an updated quote with the excuse being short-supply of units, price increase etc. Self-install? So the alternative is to self install (with electrician), but would like to keep the controller KISS and the unit install itself would need to be a relatively simple to install and connect. I've done all of the plumbing including the Willis heaters (except the Sunamps) so would like to think an ASHP install is within my grasp. Worst case, I'd have to rope in a local plumber who has some experience of installs - maximum of a day I would think? Any feedback gratefully received!

At the suggestion of Alphonsox, I've been reading the descriptions of UFH systems heated by a willis heater. I'm seriously considering using one in our barn conversion in place of the intended wood burner. However, willis heaters appear to be only for vented systems and I'd rather have unvented for ease of install. How have people dealt with this?

It's March, sunny but cold. Yesterday my PV report shows: System Production: 41.7 kWh Self-consumption: 25.74 kWh Export: 15.97 kWh So I'm exporting lots of unused electric (once my UVC is satisfied) and then late afternoon we fire up the log burner and the central heating comes on. Daft this when I could use the PV electric excess to warm up the UFH instead of expensive LPG via a Viessmann boiler. Looking through old threads I notice a reference to a 'Willis' external immersion device, never heard of that but a quick Google and it looks the ideal device especially as my SolarEdge PV control system can handle a 3kW immersion element. My local plumber knows nothing about an external immersion device, so hence some questions: 1. does it need an additional expansion vessel adding to the system? 2. if I install the device just before the ufh manifold, would extra valving be ESSENTIAL to prevent the ufh pump running the return water through the boiler circuit all the time? 3. I have a BS1820 temp sensor buried in the slab, the control circuit seems simple: if (slab temp < desired slab temp and solar PV excess exists) { run ufh pump willis unit on & powered by SolarEdge PV diverter wall socket } since the boiler will auto control itself and will back off if the returned ufh water is up to temp Failure points: * if the ufh pump failed the Willis unit dual thermostats will cut in and switch it off * if the slab temp sensor fails the floor could get too hot so an extra temp sensor on the manifold could verify the return ufh water remains within acceptable limits. Have I missed something? Or should I just stick to running round the house when the sun comes out switching on electric towel rails and fan heaters