Boilermate 0v PHE pump on continuously.

I have a boilermate 0v bma185 (2008) and last week it developed a fault. The hot water stopped working although the central heating and boiler were fine (boilermate temp sensor readings were as normal). Checking the fault codes all are FF. Anyway, I thought it had to be the PHE pump that had gone as I could hear humming but not feel it pumping water, which I confirmed by removing the large nut in the centre and the pump was seized. Therefore I drained the system and removed/checked the pump, it was seized. I bought another and fitted that thinking this would solve the problem. What is happening though is when the boilermate starts and goes through it's startup cycle the PHE pump clicks on but doesn't switch off and H2.1 stays lit. I think as the pump must have been running continuously and this seized the original pump. Therefore my question is do you know what is causing the plumb to stay on? Is it a Relay not working properly? If so how are these changed? I see you can get spares. Or Is there a delay timer that should be switching it back off again? Or is the PCB shot? I see that sensors seem to go quite regular so checking these the resistance for the dhw in and out were both 11.5 so they look ok.

As a temporary fix (so I have hot water) I have been removing the plug to the PHE pump and plugging it back in when I need a shower! This isn't the best through but keeps the wife happy!!

Many thanks

Tim

Number one check the unit is full?
Bled the pump?
Any air?
Could be sensors try flexing the wire near the brass bit gently they go there.
Could be board, Voltage at the pump?
Goes up and down or constant.
If so Main board.
Mike

Hi mike, thanks for your reply,

Problem sorted,

Once the boilermate was up to full temp, i ran the hot water for 5 mins and it sorted the issue so it must have been air in the system as you said. It's all working fine now.

Still can't understand why air in the system would have kept the pump on? There isn't a pressure sensor is there? just the temp in and out sensor and these were reading normal,

Thanks again,

Tim