Smurf is right.
However another cleaner on the other forum puts his heater before the pump. A strange way of doing it? As the pump will handle temperatures of 60 degrees, this works for him.
One could do the same but branch the hot water into 2, a pump for each operator.
I'm not sure if you could do that with a Corwoods heater, but I would follow Smurf's advise and buy an LPG tankless heater off Ebay for around £80.
Just please vent it properly.