Failed install (initial SCOP1.8), clueless installer compounded by poor support from Mitsubishi. Help needed desperately!

Bart · 2025-06-12T05:08:22Z

Hi All, My first post. I've learned a lot from reading this forum, wanted to validate my understanding and thought others might learn from my terrible experience. Having completed a 5 month complaints process and made limited progress with the installer I've now had to escalate to the scheme provider/trade association. Given apparent collusion I'm not specifically sharing details (publicly) of the companies involved at this time. Improvements reducing legionella cycle settings to minimum required (temp 60, scheduling & duration) reducing DHW to minimum required settings (temp 45, scheduling & duration) running in compensation curve setting to discover required water temps for desired internal temps for any given outside temp (45@-2 & 25@15) adjusting flow rate to maintain delta 5-8 (ie. gap between flow and return temps) Freeze stat function disabled as glycol had been added to the system All the above increased COP to 2.7 on a perfect day ie. 30% (Thank you RHH!) Problem The system was short cycling I couldn't achieve internal temp above 19+ regardless of water temp I couldn't achieve a delta 5+ even with pump running at 8l/min (manufacturers guidelines state optimal is 17l/min) and the pump wouldn't couldn't achieve 14+l/min. This suggested: the ASHP was too large for my property AND/OR the radiators were too small the pump was insufficient something else? 1. A 6kwh system had been installed. My heat loss survey=3.6 (however u values, room sizes, layout were all wrong) and it was amended (post install) =3.1 2. The installer 1st requested additional payment for a bathroom radiator, then refused to fit it, then only complied after I refused to sign off completion. However the amended heat loss survey has subsequently found that the kitchen radiator is also too small (K3 needed). 3. As yet no reply at all regarding the pump that can't achieve optimal flow rate 4. Flow/return temps don't tally with flow/return temps at the radiators. Also flow temps never fall below 25 and return temps never fall below 20. "The Game's Afoot" I queried the proximity of the design with the installer and manufacturer At the installer's insistence a sales manager from the manufacturer attended, later emailing: "all I can advise.... it's been installed as per our instructions" and sharing a document that suggests "initially setting min flow temp to 35" (erm I get it my flow temp is low but don't I get to decide how hot my house is?) "You need a volumiser- Yep like a hole in the head" In the interim 3 months the installer had decided to add a 32 litre volumiser in my loft (without my consent) on the longest radiator run in the house not on the main return (although I'd like it on flow for defrost cycles). My entire system was less than 40 litres Narrow delta continues SCOP remains 2.3 Half of the heated volume of water is now located outside the insulated envelope of my house (wasted heat not included in SCOP) Balancing radiators is a nightmare (7 vs 50 litres) The same sales manager has defended this ridiculous decision sharing the turn down datasheet HELP? The manufacturer's home help technical team have yet to respond to my request for 5kw turn down data- can anyone help? I've argued this would appear to show that my ASHP is too large, not that I need a bucket of warm water in my loft- Anyone have any resources that might confirm this please? The missing K3 in the kitchen would add volume but not much. I've argued that a pump that can only achieve 14l/min given an ASHP that requires 17l/min optimal flow isn't compliant as it isn't fit for purpose. Anyone have any resources that might help please? I've argued that flow/return thermostats that don't record flow/return temperatures aren't compliant as they aren't fit for purpose. Anyone have any resources that might help please? Thank you for reading.