no hot water

Dear all, I have a Gledhill Boilermate 2 cylinder linked to a Potterton Suprima 60 boiler - about 6yrs old. Heating works, hot water is in the cylinder, but cannot consistently get hot water out of the taps (get hand-warm for a minute or so, then runs cold again). Had a plumber in to see what he could do and mentioned the possibility of an in-line thermostatically controlled valve, but he was unsure how this particular system worked. Any advice for a total novice greatly received.
Mark

Try contacting these people,
Gledhill Building Products Limited
Unit 4, Sycamore Estate, Squires Gate,
Blackpool FY4 3RL
Tel: (01253 ) 474550

read manufactures instructions (download from web site). common fault on these is the thermistors not working there are 2; one on the pump one on the dhw heat exchanger they measure the temp of the water. they go out of calibration, you will need to use buttons on pcb to access which thermisor is faulty or replace both, note they sit in wet pockets ie drain system pessure to replace