OK, after a bit more research I have found out the water heater is a Johnson and Starley JANUS6.
AND the pilot light is out! (I was looking at the air heater before - didn't realise they were 2 separate things).
Got the manual from J&S website (thank you J&S )...
I'm a bit new to this but I think I have a gravity feed DHW system.
I have forced air heating, which still works, but no hot water.
When I turn on the hot water on the boiler I hear a click but no other noise and the pipes leading to the hot water tank are cold.
The pilot light on the...