I have had this shower installed for 6 months all ok. The shower started to fluxuate between hot and cold for 10 mins.....now cold only coming out. Suddenly pressure not as good. We have always had good mains pressure. Is there some sort of pressure limiter within the shower when it is not working. I know i have a 2 yr guarantee...but just making sure the problem is not on my side before i call them.