HW only with CH on - inherited potterton system

[KeithP]

Hi friends ..
Im currently spending the weekend with my brother who's recent house purchase also included what appears to be a gravity fed single loop boiler system ..and being unfamilliar with this setup ..I figured you guys might be able to point me in the right direction..
It appears the system is a single loop which is fed from a potterton boiler which has been installed recently-ish when a baxi was removed..
The ch loop is diverted through a helical coil inside the hw storage tank and the flow is controlled with two motorised valves..
The storage tank also has a thermostat strapped to its body ....and also has an alternative heat source (immersion element).
His problem appears to be electrical.
Basically the contoller on the wall can select HW&CH or HW / CH inedpendantly but he can only get Hot Water when the Heating is on..
Selecting HW on the controler (Sunvic SP50) lights up the indicator but the boiler simply doesn't fire up ..
In CH mode the boiler starts without a problem ..
There is no room stat in the system ....each rad being fitted with a TRV and the boiler 'efficiency' is set to max..

Can anyone point us in the right direction with this ..as he currently has to use the immersion heater whenever the heating isn't required..
rgds
Keith

 

[kevplumb]

sounds as if the h/w zone valve is not switching

see here

look at s plan

 

[KeithP]

Thanks for the speedy reply Kev ..and pointing me to the correct plan..
rgds
Keith

 

[bripl]

check the clock it may have been left on 10 programmes rather than16 recent upgrade maybe old clock set for old sys gravity h/w otherwise out with the neon/multi meter and find the culprit

 

[KeithP]

Thanks a lot for the help ..
..as usual ..very speedy and most useful info..
Fault traced to faulty switch on the motorised HW valve ...
It physically moves (motor ok) but the microswitch was permanently open circuit ...hence no power to start the boiler in HW mode..
cheers
Keith

 

[kevplumb]

h*ll trev we will have to put a block on this satisfied customer thing

 

[bripl]

tears of joy kev and we did not make a penny or rip anyone off

 

[kevplumb]

must be getting old marra

 

[bripl]

talking of old how is the dino

 

[kevplumb]

with him mate