Alpha CD30S Boiler - Frost setting

[dburley]

I have just bought a house with a Alpha CD30S boiler with a Oso 210ltr presurised cylinder but found that it runs even when programmed off - often using 25kw overnight compared with a wintertime daily consumption of 75kw. Read manual and realised there is a frost setting that kicks in at 8 degC primary circuit water temp but tested this out and system still runs even when outside temp (let alone inside/water temp) is 10-12 degrees. Rung/emailed Alpha but they appear not to be bothered to respond.

Not sure if this is "usual" or if the main temp sensor is faulty - although I would have thought if this was the case the boiler would not operate.
Has anyone any ideas?

Thanks

David B