How do I get my central heating to work?

[AMF38]

Can anyone help?
I have a BG330 condensing boiler powered central heating system. About a month ago the boiler faulted with an F5 fault relating to an Overheat.
Using this forum I was able to find the Overheat thermostat reset switch which got the boiler back online. However now the central heating won't switch on unless the hotwater is on too. I have checked the motorised valve and all is working ok, but it never moves to the ch position unless manually moved. When in the ch position the system runs for a couple of minutes then stops.
Can anyone suggest what the fault could be or what I should check? Do I need to check the Overheat thermostat or flow/return thermistor?
Any help/advice would be very much appreciated

 

[stem]

I have checked the motorised valve and all is working ok, but it never moves to the ch position unless manually moved.

So it's not working then. With hot water 'off' and central heating 'on' with the room thermostat calling for heat, then the valve should wind fully across without any manual intervention.

 

[AMF38]

Yes that's correct. The thermostat is calling for heat so it should come on, but the valve never moves over to CH without manual intervention. However even after manual intervention the system runs for a few minutes (2-3 mins approx) then stops. I can feel the radiators have started to get warm but it never runs long enough to heat up fully.
I have checked the batteries in the remote thermostat and can see the light is on at the main unit showing it's calling for heat, so when the CH heating is switched on it should run.
What do you think is causing the system to stop running after a few minutes?
The valve moves fully through each position when manual turned by hand.
I was looking to replace the midflow actuator and valve but bumped into a BG engineer in at the sales counter who believed that the issue didn't involve either part as the motorised valve moved into the mixed position
Any ideas on further tests I could carry out?

 

[MANDATE]

I had a problem something like yours and what was happening was the valve would move to mid position, so I got HW and CH.
Now the HW soon became satisfied so the valve then moved fully across to the CH position as it should but the boiler did not light.

When HW is included in the demand its the cylinder stat that provides the power to light boiler. When HW is not included or included but satisfied then the power to light boiler comes from the valve.
In my case the problem was caused by a faulty micro switch failing to close.
I think you may have similar fault
The contacts on micro switches get dirty/burned and sometimes fail to open or fail to close, either not breaking contact or not making contact.

Of course if valve does not move to the CH position then that could be due to stiff valve spindle or faulty motor or other faulty micro switch or incorrect wiring.

 

[AMF38]

Thanks for the information. So is there something I can do or am I looking at having to get a professional in?

 

[MANDATE]

It depends on what valve you have fitted.
If wiring is OK and valve spindle not stiff then the best option is to change the actuator head mounted on valve spindle. That way you new motor and new micro switches.
Also depends on your electrical experience and ability and the understanding of how these valve work.
Even with HW and CH turned off, there is still one other wire feeding the valve that is live so you have isolate the boiler totally

 

[AMF38]

I was planning to replace the mid flow actuator with an identical one and switch the wires like for like. But from what you're saying it possibly sounds a little more complex than that?
Do you think there is a fault within the electrics of the boiler?

 

[MANDATE]

As long as you remove the power supply you should be OK.
What I did last time instead of dis-connecting the wires in the terminal box was to mount a patress box on the nearby wall. fitted a terminal strip with 5 terminals for the wires(white,grey, orange,blue and green/yellow.)
The new actuator came with about a metre of cable fitted, so put this in the box from the bottom then cut the existing cable and fed this in the box same way and put blanking plate on. Just saves messing about with any other wires

You can carry out tests if you want before you spend any money. It's worth looking a the FAQs near top of these plumbing pages.