Hot Water very Hot and Heating Pump Constantly Running

[Cj900r]

Hi, I have a Worcester Greenstar 24i boiler and a Megaflow 120L Tank. The system is around six years old and was last serviced in Dec 2015. Recently the hot water has become much hotter and the Central Heating Pump now runs constantly. I contacted MegaFlow who said it was the tank Indirect Thermostat at fault which I had changed but this made no difference. The red 'trip' button had not been activated on the adjacent 'Thermal cut-out'. After further research I ended up changing the boiler PCB which also made no difference. My next thoughts are to test the Boiler thermistor, any ideas are gratefully received.

 

[picasso]

Probably the two port valve on the hot water cylinder is stuck , why don't you get someone to look at the system rather than throwing parts at it?

 

[Cj900r]

Hi, thanks for your response. The valve on the hot water cylinder seems fine and operates as it should.
I would get someone round but my recent experiences with plumbers in this area is pretty bad which drives me to doing it myself.
Any more ideas?
Thanks, Carl.