Shower Pump Troubles...

Hi Guys,

So I fitted a shower pump recently which has been working perfectly for last 2 months. I shut off the water last night to do some work in another part of the house. Nobody tried to use the pump when the water was off or anything like that, but whenever I shut the hot water off, then turn it back on the taps spit out as if there's a little air in the system or something.

Anyhow. This morning when I tried to have a shower, the shower pump would turn on but will only pump cold, even when the mixer is turned right round to hot. I'm thinking there may be a small airlock or something stopping the pressure to change in the hot pipes to activate that side of the pump? I have tried putting the shower head down low which would normally solve the problem, but still no joy!

Any ideas anyone?

Thanks.

 

Please help.