Halstead Best 50 Heating problem

[drewdrewuk]

Hi there wonder if anyone can help me, i have a Best 50 boiler that is giving me problems.
The hotwater side of it works perfectly well but the central heating has stopped working.
Symptoms are that when we turn the heating on (via the room stat) the boiler fires and a loud buzzing noise starts, i have tracked the buzzing noise down to the relay on the Aquastat PCB. This buzzing continues until the room stat is switched off. No heat gets to the radiators.

I brought a new Aquastat pcb and installed it but this has made it worse as with the new Aquastat pcb boiler dosnt fire at all....but the buzzing has gone ! With new pcb installed boiler will fire up on the hotwater side.
All ideas greatfully recieved.

 

[Gasguru]

If you are competent measure the switched live voltage at the boiler connector block...should be around 230V in hot water and heating mode. Perhaps in heating mode the motorised valve microswitche(s) are playing up and not providing the full voltage to the boiler.

 

[drewdrewuk]

Thank for the reply Gasguru, by motorised valve do you mean the one by the tank that diverts water between the CH and the HW ?

 

[ChrisR]

He does.
Sounds like it needs a new head (=actuator).
Plenty here on that, do a search.

 

[drewdrewuk]

Thanks for the reply ChrisR, should i be able to test this before buying a new valve
Can i isolate the valve to test the rest of the CH system, if so how ?
The diverter is a acl drayton mid position valve 679h340-30L0, do you happen to know if i can just replace the motor assembly rather than the while valve on these.The manual lever on the side moves freely so i don't think that the valve has seized up.
Ps
Sorry for all the questions.

 

[Gasguru]

No, start by measuring the voltage at the boiler switched live terminal. No point in buying a new valve actuator yet....the problem could just be a faulty room stat. Measure the voltage, google Y plan wiring diagram and trace the fault.

 

[drewdrewuk]

Hi there, shorted out the room stat wire and no change, also got 230v there.
When i go across the switched live at the boiler i get 170v, as GG said it should be around 230v can i assume that in all probability its the diverter valve not supplying the correct voltage ?

 

[The Baker]

Before working on Electric, check your life insurance is paid up

Tim