Electrics on a central heating system

[Eyebrowes80]

Hi Im a gas engineer and I have an ongoing problem that I think is down to the electrics. No power going from the junction box to the pump, no power to the boiler, and the room stat doesnt click. The three port valve motor was stuck but it was replaced and now motors across when there is a demand from the programmer which has power to it. All the components are wired into the same junction box but a new development is when I changed the circuit board on the boiler it blew the light switch in the room where all the troublesome equipment is. I havent touched the junction box only to visually see if there is a loose connection.
Im not going to attempt to repair any electrics on it but would like to know if anyone has an explanation as I think the problem is an external electrical problem rather than a central heating system one.
Can any one explain?

 

[bhm1712]

by blowing the light switch what exactly do you mean?

The boiler shouldnt be on a lighting circuit. Does the pump start when there is demand from the programmer for HW? or no power to the pump in any situation. The room stat should click if mechanical, and you should still here a relay operating if its electronic unless its a solid state relay.

what kind of heating system is it? gravity HW pumped heating? Y plan, S plan??

more info needed

 

[Eyebrowes80]

by blowing the light switch what exactly do you mean?

The boiler shouldnt be on a lighting circuit. Does the pump start when there is demand from the programmer for HW? or no power to the pump in any situation. The room stat should click if mechanical, and you should still here a relay operating if its electronic unless its a solid state relay.

what kind of heating system is it? gravity HW pumped heating? Y plan, S plan??

more info needed

Thanks for the response

Fully pumped y plan. Programmer switched on and no power going to pump also no power going to boiler but the micro switch on the 3 port motors across when there is a demand. After I fitted the PCB in the boiler downstairs I went up to the room whereit all was turned on the light and the fuse went on the switch. As you can see some components are getting power and others are not.

 

[bhm1712]

well as far as i can think without a diagram infront of me, the HW signal will come from the programmer and go throught the cylinder stat, which if calling for heat will put power onto the pump and boiler ignite. The output from the programmer 'HW off' will also turn off which will take power off the motorised valve grey wire and allow it to change to the right position for HW.

If your not getting any power when HW on, id suggest checking the cylinder stat is not broken or at least check to see if its calling for hot water.

In fact before you do that, have you checked to make sure there is 240 coming FROM the programmer, not just to it? as the problem is not just confined to one setting, its on both CH and HW. start with the simple thing to check.

 

[bhm1712]

unless the central heating is on a lighting circuit i fail to see how its connected...probably just coincident that there was a fault with the light switch / lamp

Another thing i just thought of : was the entire motorised valve swapped? or just the motor inside the actuator head? if its the whole thing,has it been rewired correctly??? the wiring of the MV is the difference between the whole system working or not...

 

[Eyebrowes80]

well as far as i can think without a diagram infront of me, the HW signal will come from the programmer and go throught the cylinder stat, which if calling for heat will put power onto the pump and boiler ignite. The output from the programmer 'HW off' will also turn off which will take power off the motorised valve grey wire and allow it to change to the right position for HW.

If your not getting any power when HW on, id suggest checking the cylinder stat is not broken or at least check to see if its calling for hot water.

In fact before you do that, have you checked to make sure there is 240 coming FROM the programmer, not just to it? as the problem is not just confined to one setting, its on both CH and HW. start with the simple thing to check.

There is no cylinder stat and also there is no power going to the boiler which Im most puzzled by.

 

[EFLImpudence]

There is no cylinder stat and also there is no power going to the boiler which Im most puzzled by.

I'm a bit confused.

Are you used to this work and have encountered an unusual fault or
do you not know how to do it?

It may be wired slightly differently in that some boilers switch on the pump.

You will have to test for voltage at the appropriate connections.
If there is power to the programmer but none coming out maybe you blew that as well as the fuse.
I don't know what else can be said on a forum.

 

[bhm1712]

if there is no cylinder stat its not a true Y plan.

sounds like an old gravity HW pumped CH which has been rewired to accept a motorised valve for individual control of HW and CH but without the addition of a cylinder stat- very odd. sorry but i cant help anymore as now i dont know what you are faced with unless you can post pics

 

[Eyebrowes80]

There is no cylinder stat and also there is no power going to the boiler which Im most puzzled by.

I'm a bit confused.

Are you used to this work and have encountered an unusual fault or
do you not know how to do it?

It may be wired slightly differently in that some boilers switch on the pump.
You will have to test for voltage at the appropriate connections.
If there is power to the programmer but none coming out maybe you blew that as well as the fuse.
I don't know what else can be said on a forum.

That is the case the PCB on the boiler powers the pump and is why I changed it.

 

[Eyebrowes80]

if there is no cylinder stat its not a true Y plan.

sounds like an old gravity HW pumped CH which has been rewired to accept a motorised valve for individual control of HW and CH but without the addition of a cylinder stat- very odd. sorry but i cant help anymore as now i dont know what you are faced with unless you can post pics

I think that could well be the case

 

[bhm1712]

what i dont get is the fact that systems like the one i describe rarely have a boiler with a pcb inside!!! your talking 15-20 year old G rated boilers with a simple thermostat controlling the gas valve.

Can you post pics?

 

[slup]

You can get brand new heat-only boilers and they will have a PCB in them. It is also usual on newer boilers to connect the pump to the boiler so the boiler controls the pump overrun. There's nothing particularly odd about this.

 

[Eyebrowes80]

Its an old permanent pilot/thermocouple Baxi solo probably about 15-20 years old. There is a small PCB about the size of a playing card with one connection to it that sends power to the pump. Im assuming as there is no cylinder stat that the boiler stat controls the water temperature.

 

[bhm1712]

You can get brand new heat-only boilers and they will have a PCB in them. It is also usual on newer boilers to connect the pump to the boiler so the boiler controls the pump overrun. There's nothing particularly odd about this.

Yes but its against building regs to simply fit a new boiler on a system like that.... if you have a boiler upgrade it must be changed to Y or S plan with controls for both HW and CH.

Can you post some pictures of the entire wiring centre and installation?

 

[bhm1712]

I think, as previosuly stated that the best thing to do is check for 240 coming FROM the timer/programmer as the relays inside could be blown as well