2004 Symbol--Water pump not working

Not used the van for 5 months, filled the water tank for a forthcoming trip. continuous operating noise from pump, red pump light on control panel. but nothing coming through the tap.
I fitted a new Shurflo pump about 7 years ago & it's been OK up to now. Any ideas???

Is your frost drain for boiler open?

Turn it on and off a few times rapidly to clear air and/or prime system? Someone might know if shurflo’s have seals which could have dried out