I have a Halstead Ace High boiler on which the pump has recently started running randomnly,this is with no demand at all for heating or hot water. We first noticed this happening when we woke at 5 in the morning and the only way to stop it was to turn the mains isolator to the boiler off. After a while we put the power back on and the pump continued to run but only for a couple of mins and then it stopped.. The last 2 days I have come home from work to find the pump running (who knows how long for) when everything was normal in the morning when I left the house. I have found that running the hot water for a while seems to make the pump cut off after its normal over-run period. Can anybody help?