Ariston SX20 Euro Combi Hot Water Problem

[CG56]

I have a problem with DHW on Ariston SX20. It fires up as soon as hot tap is run then about 30 seconds later burner turns off then 10 to 15 seconds later fires up again. This continues on and off as long as hot water tap is open hence water never gets really hot just luke warm. Central heating runs fine with no problems. In DHW mode the diverter valve is working, pump running and the water pressure seems fine. Any clues to what is causing this?

 

[Agile]

May be a blocked secondary heat exchanger.

 

[CG56]

Thanks for your reply. Any way to "unblock" this or is there any test I could perform. I replaced the diverter valve with a new repair kit and noticed there was a reducing washer which went on the secondary heat exchanger inlet. This seemed a little bit smaller opening than the original - could this be a problem? Should I replace with a larger one.

 

[DP]

Thanks for your reply. Any way to "unblock" this or is there any test I could perform. I replaced the diverter valve with a new repair kit and noticed there was a reducing washer which went on the secondary heat exchanger inlet. This seemed a little bit smaller opening than the original - could this be a problem? Should I replace with a larger one.

No is the simple answer.
Do you have limescale issue in your area

 

[CG56]

No limescale issues in this area.