gainsborough shower spulttering

[johnnyblue]

Hi any advice , got a gainsborough 8.5 s.e .
Had a shower tonight no problem , my daughter then went for one and the water was just spultering as if a air lock , checked inlet filter that was fine ...it makes a noise as if water is trying to get through , splutters out piping hot water even on cold setting and just spluts a bit at a time out.
After checking filter etc it did run fine for a good 5 mins , i put the cover back on happy it was cured , tried again and spultering again , can anyone help...all other taps etc working fine in the house (is it possible i have a air lock)
Just was fine when i showered tonight then 5 mins after this started?

 

[johnnyblue]

Anyone please advice , about to order a replacement from gainsborough but worried i will have same problem if its a air block or similar .

 

[seco services]

Tried running it with the head off ?