BIASI 28S shutting down after use

[sugs04]

I have an inconvenience with my BIASI 28S Combi. It cuts out after being used for hot water. The little red nipple button pops out and the boiler stops firing.

3) Has ANYTHING else been done / changed recently
A couple of weeks ago, I added water to the system to repressurise it using the filling loop. The system is just under 1 bar currently ( slightly dropped from where it was after refill). I also bled the radiators.

4) When did it (problem) start
It has been happening fairly intermittently (once every few months) for the last couple of years but it has tripped out 3 times today. Usually more in winter but this could be because the system is used more then.

5) When does it happen? eg, heating coming on or going off
Normally just after the hot water has been used I think (e.g. shower). It may have happened when just the CH had been on but I'm not sure. It does not seem to happen during use.

The temp settings for hot water and heating are both about middle of the ranges - If I turn them up I think it happens more.

Thanks in advance for any ideas.

Sugs

 

[Agile]

Are you a school Science teacher?

Warning, if you keep on resetting the overheat stat more than about 15-20 times it will need to be replaced.

Run the boiler at 1.5 Bar cold !

The problem is caused by lime scale deposition in the primary heat exchanger because your installer did not set the heat output to match the rads dissipation.

The lime scale can be removed using sulphamic acid but that needs skill and care.

You can immediately halt further lime deposition by opening the lower PCB cover and turning the R1 potentiometer marked RISC anticlockwise almost to the minimum.

Did it ever make a noise like a jumbo jet?

Tony