Suprima kettling?

[Liverpool-Lad]

Hi folks

I have a '98 Suprima 40 and hot water cylinder (3 port valve), after approx 5 mins from cold and selecting hot water I get kettling symptoms (some fizzing/mild clonks) from about 60c to 70s.

I have measured the temperature on the outlet with an infra red thermometer & the thermistor stat is kicking in at 70c. There is approx 6-7c difference on the inlet/outlet also measured near the outlet pipes.. Pump speed changing to 3 (grundfos) helps a little but the issue is still there. The main PCB has been changed in the past also.

I did try x200 last year but it made no real difference. Other than that the boiler works fine.

Any suggestions?

 

[cross thread]

Possibly restrict,try running a magnet around your heating pipes near the pump,if it sticks it has a restriction starting,

 

[Liverpool-Lad]

Thanks for the reply, nothing obvious around those pipes at all. I should mention the 'coolant' is also clear when I added the X200.