shower and hot water not working

[adamc108]

I have a one bedroom flat with a header tank and hot water cylinder powered by a baxi solo 12 HE. There is a salamander whole house pump for the shower and all the taps (except kitchen sink cold). The pump takes the hot water from the cyclinder via an essex flange and cold direct from a 42 gallon header tank above the cylinder. The radiators (4) are on a sealed system with an expansion tank.
Im having trouble with the hot water from the taps and the shower. The central heating is working fine. The kitchen mixer tap runs really hot until it fills about half the sink then goes lukewarm then cold. If you turn it off for a minute then back on it will do the same again (Cylinder is fully heated and full). The bathroom sink mixer tap will only get luke warm when turned on to hot and stays lukewarm. The bath taps which are not mixer seem to work fine and you can fill a bath with the hot water cyclinder. The mixer shower is competely cold.
I have tried a few things so far-
Turned off the cold water going into the pump, this allows hot water to come out of the shower at the temp it is set on the cyclinder thermostat but there is no cold water to any taps obviously, except the kitchen sink which runs off the mains.
If i turn off the pump the mixer taps seem to work again including the shower but pressure is not enough (reason for pump in the first place)
I have covered the kitchen mixer tap and opened it half warm to force mains cold water through the hot water pipes to get rid of any possible airlocks (while the pump was off).
None of these things have worked and i am stumped as to why the shower and taps wont work properly when there is a full cylinder of hot water and working pump.
Any Ideas? Everybody i've asked so far just says rip it out and put in a combi but i've just put in the current boiler and pump last year and spent a lot on this system.

 

[rocketmanbkk]

Did it ever work properly?

 

[wiggers]

Sounds like a problem with un-equal pressure going to hot outlets as you say your taps are fine just your mixers cold may be just be pushing against the hot maybe try putting a check valve on the hot for starters?

 

[adamc108]

yea it worked for a year and a half.

 

[rocketmanbkk]

Anything changed?

Don't be shy in giving info mate

 

[Unregistered]

the tenants think its stopped working since they turned the central heating on for the first time this year. he also bled the radiators. He topped up the expansion vessel as well but left the water feed on and it exploded and we had to get a new one fitted.

 

[PhoenixServices]

Sounds to me like a mixer tap or shower non return valves letting by and overpowering the hot.

 

[adamc108]

Would that still happen if the hot and cold feeds are at equal pressure? they come from a twin impeller pump, both 1.5 bar

 

[adamc108]

Yea PhoenixServices it was the thermostatic mixer cartridge in the shower that had failed and was letting cold water be pumped through to the hot side of the system. Replaced it and all is back to normal, thanks.