Worcester Motor running constantly but

[Bosch Sauce]

Worcester Boiler. Really annoying.
All works as it should fine in normal use. However have to go away for a couple of weeks at a time. I put the boiler in holiday mode 5 degrees it's very unlikely it's needed to kick in. When I come back the boiler pump motor is often running even though it was dormant when I left and switches on off ok in normal circumstances as it should , the pressure will need topping up slightly after that away period. What causes this? When I'm here there is never a problem, only when I leave it empty for many days. Appreciate anyone's help.

 

[ChrisB1982]

Could it be you only notice it after you’ve been away? Is there a preheat function turned on? What type of boiler?

 

[Bosch Sauce]

Could it be you only notice it after you’ve been away? Is there a preheat function turned on? What type of boiler?

Thank you Chris much appreciated it only happens after I've been away Worcester Green Star Cdi 28i ?. The boiler only goes into this state when I'm away. So for example it's not been on at all for heating or hot water in last 16 hours. It's all fine pressure retained for the last few days anyway, and no pump is running. Yet twice when I leave it in holiday mode for 14days or so I come back the pump is running constantly and the pressure has dropped. Any suggestions welcome. I am wondering if somehow a slow leak means the primary circuit looses pressure the change in pressure activates the boiler to fire up on the hot water side even though taps are closed, and the boiler mainly filled with air just churns trying to dissipate heat unsuccessfully after overheat shuts it down...and it repeats that cycle. If you switch power off and return it. All works as normal. Obviously need to trace loss of water but very old pipework and complex house such a slow loss that's just about impossible. Anyway hope you have some 8deas very grateful