hot water problem

[freakzzonb]

I wonder if anyone could help me if possible. My sister has a Vokera Linea where she has a problem with her hot water but the heating is ok. Appartently she is her hot water gets warm initially but then runs cold then warmish briefly in a continuous cycle The boiler does light up briefly and then goes off and it seems like its reaching temperature quickly but not sure what the possible causes could be

Any help or suggestions would be appreciated thanks in advance

 

[McCombi]

Most likely plate heat exchanger dirty and needing replaced

 

[freakzzonb]

cheers for the advice

 

[McCombi]

There’s a way you can check if overheating.

The display shows sensor temperature of heating when no hot water is running and shows hot water temperature when tap running.

The black lever on far right pipe which usually points upwards when not isolated can be turned 90 degrees to isolate water flow to tap from boiler.

Whilst running hot water, watch to see when burner cuts out, soon as it does quickly put the black lever to horizontal position, this stops demand and the display will revert to heating temperature inside boiler, if it reads 90 roughly then it’s showing that the boiler is ****ting down due to overheating which is usually due to plate heat exchanger being restricted.

Good luck.

 

[freakzzonb]

thanks I will try that and see what happens. Appreciate your help with this

 

[ianmcd]

If it does this it could be the non return valve in the plate Heat exchanger has disintegrated, but correct advice from @McCombi

 

[freakzzonb]

cheers