Very Old Boiler Question - Thorn M44/54C (Heatslave 2+)

[Pablo79]

I've just moved into a run down old house. The boiler, a very old Worcester Heatslave 2+ (Thorn M44/54C), works well. However, the hot water is HOT. Far too hot. There doesn't seem to be anything on the boiler I can adjust. Could this be a faulty stat?

I'm knocking the house down in 4-5 months, so I'm not looking to replace the boiler. However, if there's a cheap part I can replace to keep this boiler running over the winter and not taking my skin off, that'd be great.

 

[stem]

If it's a very old system (over 40 years old) likely it will not have a thermostat on the hot water cylinder controlling the hot water temperature in conjunction with a motorised valve. That would mean that the boiler will continually heat the hot water cylinder until it eventually pretty much reaches the same temperature as the boiler. It will waste a lot of gas as there won't be a boiler interlock that shuts the boiler off when the hot water cylinder is heated, it will run continually. This is not a boiler issue but a restriction of the plumbing system.

If it's a newer system (Post 1980) or has been upgraded since installation, then there should be a thermostat on the hot water cylinder that controls the temperature of the hot water by closing a motorised valve which stops any more water from the boiler reaching the hot water cylinder. The thermostat should be about 1/4 to 1/3 of the way up the cylinder. See pic below. If you have one, lowering the temperature set on the dial will reduce the temperature of the hot water.

If you don't have a cylinder thermostat, you can lower the boilers thermostat and that will reduce the temperature of the water feeding the hot water cylinder. The drawback here is that when you are using the central heating, the radiators won't get as hot either. I can't find a photo of your boiler to know where the boiler thermostat is, but it will be there somewhere. If you can post a photo of the boiler someone may be able to advise.

One last thing to check. If the hot water cylinder is fitted with an electric immersion heater as a back up, check that it's switched off.