No Hot Water

I have an Ariston Euro Combi Boiler SX20.
I have had an on going problem with my hot water only working when the heating is on. I have changed the diaphragm on the diverter valve and checked the triple micro switch on top of the diverter valve.
I have now noticed that opposite the diverter valve on the left of the boiler is another component with a pin that switches a single micro switch. When the hot water tap is switched on this pin fails to rise all the way to the switch, probably only by a few mm, but when the heating is switched on this pin rises fully.
Could anyone please tell me what this component is and how do I fix it.

Many Thanks

Garry

System flow switch.

If you run hot water and then manually operate that switch it should bring on the burner.

There is reduced system flow. Most usually because of a blockage in the plate heat exchanger but can also be caused by a weak or blocked pump.

First inspect the pump impeller and next remove and PROPERLY clean the plate heat exchanger.

If neither of those fixes it then there will be a blockage elsewhere in the boiler!

Tony

Many thanks

I'll give it a go.