No heat from underfloor heating

[Cheshire Gas]

I was asked to have a quick look by a friend the other day as to why his underfloor heating has stopped working. The only way they are getting a reaction at the moment is if they leave it on full wack for 3 days. Straight away I noticed that no heat was getting past the mixer valve next to the pump for whatever reason. I called a friend in who is a registered fitter and he basically said change the valve. I just want to see what you thought before I went along with this and got him in, it is literally boiling hot one side and nothing on the other! He also said it has to be like for like so I would have to find out the same make, is this true?

 

[Nostrum]

Might be worth checking the inlet filters for a blockage or similar? Drain down and whip it out.

 

[Puddle]

Can not see why it has to be the same make,maybe he meant get the same as fittings to pipe work should hopefully be the same for ease of replacement