Thermal Store Hot Water Issue

I am currently in the process of refurbishing my downstairs bathroom and in doing so, i had to close the main stop cock to isolate the water. Upon opening the stopcock back up, the hot water will now only run for circa 20 seconds and then go cold. This happens at every hot outlet.

The hot water is generated by a thermal store system. I have checked the temperature of the hot water coming out of the TS and it is very hot however the water coming out the blending valve is lukewarm. I removed the blending valve to see if it had any debris in it however upon inspection it looked clear. All ports on the valve seemed to be working too. In addition to this i also repressurised the hot water expansion vessel.

Does anyone have any advice on what is causing this and any remedies to resolve the issue?

Thanking you in advance,

Is the water straight from the store into the blending valve very hot after running the hot taps for 20s?
What store do you have?

Yes the water coming from the store is extremely hot going into the blending valve.

The store is an Albion Mainsflow direct system.

You probably need a new blending valve. Try winding it fully both ways first and then attempt to set it to give hot water. These valves do fail though from time to time.