Ariston Microgenus 27 not turning off

[Daveha]

Hi, my old microgenus 27 MFFI has a bit of a problem. Intermitantly, when the DHW is run and turned off, the boiler continues to run. The water temp goes up and the burner shuts off, as the water cools down a bit the burner comes on again, and on it cycles.

I can stop this by pulsing the cold tap on and off, and then the boiler shuts down properly. I suspect a faulty DHW flow switch ? any ideas ? Apart from this its working fine.

p.s. I've had a look at the parts list in the servicing handbook and I can't see the DHW flow switch listed ?

Thanks. Dave

 

[Paul Barker]

there are two brass manifolds either\side of the plate heat exchanger one on the left which is the diverter valve and incorporates a magnetic read switch as the primary flow sensor. The other on the right hand side which has on it's left most section the DHW flow switch. Part No. 999075 Inside the manifold is the DHW Actuator kit part no. 998941. This may simply need taking apart cleaning and replacing.

 

[Daveha]

Paul, Thanks very much for the info. I will have a peek inside the boiler tomorrow and see if I can identify the switch and actuator. I don't mind touching the water side of things.

Thanks again, Dave