ColB

I can recommend SEHPS based in Perth who put a Vaillant in for us last year, they're MCS registered and we're happy with the install.

When the outdoor temp is lower than the bivalence point, the backup boiler kicks in. If yours is set to -15 then I don't think it was your issue. Worth watching this video and compare the suggested settings toward the end. https://www.youtube.com/watch?v=3KVs7oHynEM

Hi Ady, What's your 'Heat bivalence point' set to? Might want to make sure it's set to -20 if you've got no backup heating system.

Hi Ash, The prices are on City plumbing’s online store. https://www.cityplumbing.co.uk/Vaillant-Arotherm-Plus-12kW-0010037215/p/477552?uiel=Desktop

It's mentioned in Vaillants brochure on the Saltire.co.uk website in the following link https://saltire.co.uk/wp-content/uploads/2020/09/Vaillant-B2C-aroTHERM-plus-leaflet.pdf On page 4:- "190 litre cylinder capacity delivers up to 380 litres of hot water for up to five people including the use of rainfall showers." I'm not sure about the UniTower, however we're getting a 12kW aroTherm Plus and Unistore 300L Unvented Cylinder installed in the next week or two into our new build located in Fife. We'd been struggling to get a Mitsubishi EcoDan for months because of shortages so in the end we plumped for Vaillant who only had one left in stock. I'm no expert but the plus points for us with the Vaillant is that it uses a different refrigerant (R290/propane) over most other ASHPs so can manage higher temperatures, plus a coding resistor can be installed quite easily so it can also cool without affecting RHI Hope this helps. C.