Vokera combi boiler very rapid cycling

[Thomato]

I found a post on here with a similar problem and have been advised to start a new thread as this is for a different brand. This looks a very good site!

We are having a big problem with hot water supply to taps and the shower, especially upstairs.
Hot water will heat rapidly then go stone cold after just a few seconds before cycling to hot again, repeating ad infinitum. It makes showering very difficult and uncomfortable!

The boiler is a Vokera Unica 32HE combi boiler that's been fitted for about five years in a very hard water area. I suspect the heat-exchanger is blocked and so not running efficiently.

Can anybody give any thoughts or advice on this, please? I don't want to disassemble a system if it might be just a stuck valve I haven't spotted!

Many thanks.
Thomas

 

[CBW]

Hi Thomas,

I suspect you are correct as it can’t disspipate the heat from the boiler quick enough, but you shouldn’t rule out other possibilities, such as the pump or diverter valve.

 

[ianmcd]

With the Heating cold, run a hot tap and when the boiler fires, feel the heating flow and return and see if either heats up, if they do it is a divertor valve problem, if not yes likely your plate HX is scaled, your boiler is a decent enough boiler but really must be serviced properly every year and not just a poke and go with a flue gas analyser.

 

[Thomato]

With the Heating cold, run a hot tap and when the boiler fires, feel the heating flow and return and see if either heats up, if they do it is a divertor valve problem, if not yes likely your plate HX is scaled, your boiler is a decent enough boiler but really must be serviced properly every year and not just a poke and go with a flue gas analyser.

I ran the tap and checked all pipes to be sure I hadn't got the wrong one and only one pipe heated up.
By your post, I think that's the heat exchanger found out.

Thank you!