softened water and filling a cast iron boiler with modern unvented

[cypher007]

is it ok or even a good idea to use softened water in a central heating system? this is partially related to another post. the heat exchanger is iron, but it feeds via an indirect coil an RM stelflow unvented. will using softened water cause corrosion?

 

[steadyon]

Most boiler manufacturers advise against using softened water. Most water softener manufacturers say it is OK.

Two years ago I changed my own cast iron heat exchanger potterton. It had been running on softened (Permutit) water for 27 years with no ill effects whatever. However the cylinder and coil as well as all the pipe-work in the system are copper.

The Stelflow cylinder is, I believe, stainless steel, with a stainless steel coil. There may be a risk that the very slight traces of salt present in softened water could cause corrosion. Have a word with RM and see what they say.

 

[Sparkgap]

Probably not. Unless you have a leak once the water is in the system it stays there and any corrosion would be unnoticeable. Best if you put some inhibitor in as well to make sure.