Unvented Cylinder Help please

WaywardDriver

Water was off yesterday due to burst mains pipe and restored after a few hours. Afterwards all seemed OK with house water, until following morning when shower was used. This is fed from a direct mains unvented cylinder (Albion Ultrasteel Indirect) linked to an oil boiler. Inspection showed cold water flowing freely through the tundish to the outside overflow.
My knowledge of these systems is minimal and I have no intention of meddling with things I don't understand, but could the surge in pressure when the mains came on again have triggered some safety mechanism in the system?
I'm having some difficulty locating a suitable heating engineer (in Northern Ireland) and before trying again and running the risk of unnecessary expensive repairs, is my diagnosis plausible? Also is there a separate stopcock to turn off the system without turning off the main stopcock which I've done? - none obvious to me.

AndyPK

mine has a stop tap near the tank.

So its flowing out even when the tank water is cold ?

My tundish has 2 pipes into it.

1) from mains pressure reducing valve
2) from the top of the tank.

System

The most likely reason for water flowing out through the Tuni Dish is a loss of pressure in the cylinder. Before calling an engineer it is worth attempting a recharge. This involves nothing more than turning off the water supply; turning on a hot tap below the cylinder and holding open the T and P valve until water stops flowing out of the cylinder. This video might help:

https://www.youtube.com/watch?v=1nuXmayzIac

I should add that to get a full recharge you need to hold the valve open until all the gurgling stops. This can take 15 to 20 minutes. You then open the stop c**k! and turn the hot tap off once you get a flow of water. I recharge my cylinder every year.

WaywardDriver

Here is image of my setup

The vertical copper pipe in the centre goes to the tundish. Am I correct in assuming the lower red valve is the pressure relief valve which needs held open until water stops flowing?

System

WaywardDriver wrote: »

Here is image of my setup

The vertical copper pipe in the centre goes to the tundish. Am I correct in assuming the lower red valve is the pressure relief valve which needs held open until water stops flowing?

Yes, do not fiddle with the grey one as this is set at 3 Bar. The lower -red - valve is just a relief safety valve which opens if the water in the cylinder gets too hot or the 3 bar pressure reducing valve fails (ie, the pressure in the cylinder gets too high).

You will need to twist the red knob and hold it in the open position under all the glugging noises stop. All you are doing is allowing air to enter the upper part of the cylinder to provide a bubble at the top of the tank.

This may or may not work. I had to have the 3 bar PRV replaced on my cylinder last year as it wasn't holding the required pressure and my thermostatic shower was running cold.