Main Eco combi 30 DHW Problems

[RoryD]

CH works ok.
When there's a demand for DHW the boiler fires, modulates and then stops. The process then continues in this fashion ad nauseum.

The flow pipe from the Heat exchanger doesn't get hot, the pump continually "surges" on/off and gets very hot.

When the preheat kicks in the pump turns fully with no difficulty, the burner fires away as normal, however the red light is illuminated on the Hall Sensor??. The moment a DHW tap is opened the fault starts immediately.

Faulty turbine has been changed (was flickering) and the DHW sensor has also.
Calorifier has been washed through and there was some magnetite.
The pump is a "low energy" pump as marked on the front.
I'm trying to get my brain cell around the preheat circuit and the normal DHW circuit. Why is the red light on the Hall sensor during preheat?

 

[RoryD]

Thanks for so much...feedback....not! For anyone who may venture into here, Plumbs gave me the incorrect Flow Turbine. In fact for this model the there's no turbine (hence the slightly different appearance of the new part). I neglected to mention the boiler was a Main Eco Combi (of which, there are two models??!!) Because I had a "Spinning" Turbine as opposed to a magnetic "lifting" sensor which looks similar, the boiler was behaving in the above manner. This is called a "filter" on this model and has to be purchased as a whole inlet block.When the correct part is fitted the boiler operated normally (surprising eh?)