I dealt with them ~12 years ago when I had an excellent proportional control Dru gas wall heater*. They were very helpful, but sadly the heat exchanger for it was no longer available. (I don't know how old it was at that point.) Neither did they any longer do a 4.5kW heater; only smaller ones for home use or bigger ones for commercial use. Otherwise I would probably have bought another to replace it. Anyway, that forced me to install central heating.
*After I'd pulled the thermostat phile out from behind the heater so that it wasn't self-heating, it was maintaining the room temperature stability to within a tiny fraction of 1C. It was easy to add remote control by sellotaping a couple of resistors to the phile to generate setback, and it worked in power cuts as it had no electricity supply.
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