Gas boiler heating problem

[William Clements]

Heating is done by a gas boiler,(old but works well) and water is heated via an indirect coil in the cylinder with a thermostat on the exterior about 2/3 way up from the bottom. I can never seem to get the temperature of the hardware right, it is either far too hot or just warm enough, it is noticeable when the shower is in use, I have to turn the shower control way down or full up.
My first thought was the cylinder stat, so I replaced it, but no difference.
The issue happens in the summer as well when the central heating is off, and the boiler is only in use for hot water supply.
Obviously, when it is too hot I am wasting gas, not good. Need suggestions on this or else should I call plumbing repair service?

 

[Paul Sweet]

I'm afraid it's the nature of the beast. A separate domestic water heater is your best bet.

 

[William Clements]

I'm afraid it's the nature of the beast. A separate domestic water heater is your best bet.

Thanks

 

[HForester]

Run the thermostat higher than you need and put in a ASSE 1017 tempering valve to control (limit) the temperature to the hot water distribution system. This is the way it has been done ever since Holby valves came to be in 1930. I am not saying that Holby is the brand of valve you need to use but they were probably the first ones to design such valves (in the US). Many other brands are available.

 

[jwilly3879]

This is also called a tempering valve.

 

[HForester]

that's what i said: "a ASSE 1017 tempering valve" per IPC Section 613.1 (2012 edition)

 

[Master Pipe]

You can see your gas boiler heating changed.