Loud Running Water Sound Going Into Hot Water Cylinder

Anon

I hope someone can offer advice please.

A few weeks ago we had our boiler replaced (conventional boiler - now a Viessmann 100). Since that time, we have had the sound of running water in the airing cupboard whenever we have put on the boiler to heat the hot water (it doesn't do it when heating the radiators). We don't recall it being this noisy before replacing the boiler.

The water cylinder is a Tribune Premier model TP150B 150 litre. There is only a single tank in the loft which appears to have mucky water in it.

From following the pipes, it is the hot water pipe going from/to the pump, past an automated valve (I assume that is what it is called - an electric controlled gadget attached to the valve!) to the tank.

Any suggestions please? We don't seem to have as much hot water available after having it on a few hours as we used to, which may also point to a cause. I have assumed that if we can hear the water flowing the is not full and possibly air in the system? All radiators have had the air released but it doesn't seem to be that part of the system.

Thank you.