mixer shower cw prob

[w1nxn]

fitted ensuite couple months back, had call from customer telling me no c/w coming from mixer shower occasionaly, only hot (concealed mixer). investigated to find c/w will run but not everytime shower turned on.

turned mixer to cold, turned on shower, no c/w. went into bathroom and turned on c/w bath tap suspecting airlock ('T' from shower c/w feed), shut with thumb, and hey presto shower runs with c/w and shower runs fine, then once turned off/on will only run hot again. surely if this was an airlock then it would release once both bath c/w and shower both on and running fine?

pressure required for shower min 0.1 bar which it has 1.5 metres head so ok. h and c have same pressure as from cws and no sign of debri in cws either. im now left with thinking theres a blockage in c/w feed from cws that releases when i work bathtap or i may need to raise cws to gain further head pressure which i will obviously have to charge for but considering i supplied the shower that may not be an option.

please tell me im missing something so simple that its too obvious lol....

all comments gratefully recieved (even if im questioned about my ability as seems to be happening often on here) hehe.

and breathe...............

 

[REDSAW]

i whould start with th cws, it sounds like its in suspension/blocked restricted.
try jetting backwards into tank with caution so you can see what goes into tank.

if you leave the cold on for a long while, a slight discharge of cold will confirm thos.