Back to my problem

An update is this.
Thermistor taken out of pocket and left hanging in clear air, temp probe inserted in pocket that can be read externally to the boiler.

Boiler fires and keeps firing until the mid store temp hits 77 and bingo the sytem shuts down the boiler. The temp in the thermistor pocket reached 108 degrees, is the sort of temp one would expect the cast of the heat exchanger to reach in raising the water temp from 65 degrees to 77 degrees? It probably took about 15 mins approx.

Stephen

Hi Mike.

Late reply I know, yes I think I found the problem and worked around it, see my explanation to a query this morning.