Mixer taps, no water, hot or cold

WIAWSNB

UncleZen, we need a pic of this tap.
If it's 'ceramic', then we'll need to explore the supply to it as the likely cause. If conventional 'washer', then the tap itself is faulty and needs dismantling or replacing.
Is your DHW (oops, sorry - Domestic Hot Water) system supplied from a CWS (argh - Cold Water System) tank in the loft?

molerat

OP said it usually does a few turns.  One of mine that is rarely used does that.  Likely a strip down of the cartridge and lube the threads with some plumbers silicone will fix it, just "working it" will probably give a few weeks relief. But if you can't do it yourself it is a bit expensive paying someone as it is an all labour no parts job but also something a plumber wouldn't want to do as it is not a guaranteed fix.

UncleZen

@danrv thanks. I think there are isolation valves, I'll have a look.