hot water goes cold

Hi
Tha hot water starts off hot then goes cold and after awhile hot again, the sensors seem o k if you follow the procedure described in the manual,the temps on the high and low side are 76--46 degees and the store temp is 75 degrees
would be grateful for any ideas

Thanks

Dave

A failing DHW sensor is the usual problem, but that low reading of 46 degrees is FAR too high. This suggests your heat exchanger is clogged up with water scale. I think a new one will fix it.

Cheers, Mike

Hi Mike
Thanks for your advice, is it worth changing the sensor(cheapest option) or just change the heat exchanger,any idea what the temps are supposed to be at the sensors?

Thanks Dave