Expansion Tank Pressure Constantly Dropping

several problems ,is it a megaflow ?,the brand megaflow does not have an external expansion vessel,what colour is the expansion vessel ?,i would assume it is red,this will be the central heating expansion vessel,you could have a faulty prv or the expansion vessel needs topping up or replacing,if you live in a hard water area you will get this scale build up in pipes ,cylinder ,showers etc,you may need to fit a water softener.

This is all caused by calcium carbonate that is present in hard water, which then is a build up.of limescale ,, it will build up faster on hot water appliances. This is because hot water evaporates off a surface much quicker than cold water would,,so it will cause mineral crystal ,,build up in strainers etc and as for the expansion air gap try recharging it...or if not its broken ring megaflow. Some cylinders I believe have a 25 year warranty?? In hard water areas a good strainer and a good water softener will prevent a lot of these problems ..not 100 percent but the appliance should last a lot longer than with.out the softener and a good strainer

Good Morning, The mega flow cylinder has an internal expansion vessel it does not have a pressure gauge. The client is certainly not pressurising this cylinder. If the cylinder has no pressure on the internal expansion vessel then this will lead to low water pressure. However this may not be the only reason for low water pressure. A qualified and experienced installer and service engineer need to fault find on this cylinder to identify the issues. This client can only be pressurising the heating system. If the pressure on this is continually dropping this indicates issues with the heating system. Again any faults on the heating system can inly be identified by and experienced and qualified engineer in accordance with manufacturers advice and instructions. The "Mineral" identified is lime scale this is produced when water is over heated, so the boiler and cylinder thermostats need to be checked. More lime scale is created the hotter the settings. The client needs either a water softener or more economically a couple of water strainers to stop limescale entering the system. Unfortunately the client is making the situation worse by trying different incorrect methods to resolve the issues. Hope this helps. Thanks for your time. Colm Senior engineer H2O

The pressure loss could be a fault with the expansion vessel or pressure reducing valve, check if any water is passing through the tundish when the boiler is heating the water, the low hot water pressure might be a blockage in the filter in the pressure reducing valve, you really need a engineer qualified in unvented cylinders to check and repair as needed.

Megaflo Cylinder have internal expansion vessel . Normally the title expansion vessel Tank is for your boiler . Depend on the boiler types and systems . The most likely problem either a leak or the vessel has failed . Check for leaks and the discharge pipe outside . Hope this help . Johny