Vaillant Turbomax loosing water pressure

[John]

Hello folks,

we have a Vaillant Turbomax at the Scout Hut which has not been the most reliable, however the current issue is that the water pressure drops on an irregular basis! There are no obvious leaks but some evenings it is down to 0 - when we fill it up the pressure seems to hold (and the boiler works), it may then be OK for a week before suddenly dropping to

2. I suspect the Pressure Relief Valve since the relief pipe seems to always be wet and there is now moss growing on the path underneath the outlet, but I would value expert opinions.

[Andy Hall]

This can be because the pressure vessel is on its way out. You fill the system, it gets hot, but instead of the water going into the vessel it is expelled through the valve.

It may also be that the valve is crudded up.

If this is a boiler with integral pressure vessel, then it should be possible to effectively "abandon" it unless it has corroded through and is leaking. Replacing these is usually more expensive than an external pressure vessel.

Often the least expensive solution is to install a sealed system kit consisting of a pressure vessel, manifold, pressure gauge and relief valve. These are sold as a package for quite a bit less than the sum of the parts. One of these could be fitted in place of the existing pressure relief valve.

[<me9]

Little fingers on PRV?

How much does the pressure rise when the system is fully up to temperature? It may be a pressure vessel with a lack of charging air. See sealed system FAQ.

It could also be a leaky pressure relief valve.