Discuss Heating Engineer hasn’t been able to diagnose WB 30CDi stalling in the Central Heating Systems area at ElectriciansForums.net

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I have a Worcester Bosch 30CDi that only intermittently heats the house. To get it to do so when it stops, I sometimes can kick it into life by turning the room stat on and off rapidly, sometimes by turning the programmer on and off rapidly, and always by going up to the airing cupboard and turning the HW thermostat up. Doing these things will make the pump start. Otherwise the pump doesn’t run (except if we use a lot of HW, of course)

The motorised valve on the heating is in its sleep position when the boiler is stalled, the position in which the lever on the side does nothing. Once we get going the valve opens up.

The valve on the HW seems to work fine.

The room stat is a Honeywell T6360, and I’m about to replace that, because for a while a few weeks ago flicking the existing one on and off reliably started the pump.

The programmer is a Honeywell ST9400C.

My money is currently on a fault on the boiler pcb but my heating engineer doesn’t seem to think so (but hasn’t come up with any other idea)

Help, please! Thanks for any thoughts.
 
Hi - there are electrical tests to see if the thermostat, programmer and valves are giving the correct input to the boiler. Without the right voltage at the right time the boiler won't start, or won't turn off when you want it. You may have a micro switch problem in a valve (for example) that only sometimes is sending L through to start the boiler.
 
Could be a faulty programmer, stat or valve. I don't think it's a fault with the boiler as the HW Valve and controls are working correctly.

A spark who is comfortable with heating systems would easily be able to diagnose the fault, rather than guessing and replacing all control items until the faulty one is replaced.
 
The pcb's normally go within the first week or so, or if the boiler has suffered damage. The electronics don't like moisture, so if theres been a leak at some time it might only now becoming a problem.
A good spark could bridge out the thermostat and/or programmer without replacing to see if it still has a problem.

You say the motorised valve isn't moving when it should?
Gentle tap with a hammer usually helps.

Can you tell i'm not a heating engineer
 
I would suggest replacing the battery in the programmer. Lithium CR series, usually CR2032. I have had this problem several times, but not with Honeywell - never fit them.
Even just taking it out and cleaning the contact area can solve the problem.
 
Micro switch failures in valves are VERY common these days .....

You need somebody who confidently understands boiler wiring to fault find this properly .....

Had anything been changed on the system before you noticed these issues?
 
The first place I would personally look at is the Heating valve.

Measuring the voltage at the valve will determine if the valve is actually receiving voltage, when your heating is calling depending on if you are or not determines if you should be looking at the controls, valve output or boiler
I agree with Murdoch Microswitch failures are very common,
 
Do you hear a click when when the programmer calls for heat on heating or hot water? Can you see the green light(s) on but don't hear the click(s)? If you don't hear them the programmer needs replacing as the relays fail quite often in that model. That is the first place I would look.
 
I have a Worcester Bosch 30CDi that only intermittently heats the house. To get it to do so when it stops, I sometimes can kick it into life by turning the room stat on and off rapidly, sometimes by turning the programmer on and off rapidly, and always by going up to the airing cupboard and turning the HW thermostat up. Doing these things will make the pump start. Otherwise the pump doesn’t run (except if we use a lot of HW, of course)

The motorised valve on the heating is in its sleep position when the boiler is stalled, the position in which the lever on the side does nothing. Once we get going the valve opens up.

The valve on the HW seems to work fine.

The room stat is a Honeywell T6360, and I’m about to replace that, because for a while a few weeks ago flicking the existing one on and off reliably started the pump.

The programmer is a Honeywell ST9400C.

My money is currently on a fault on the boiler pcb but my heating engineer doesn’t seem to think so (but hasn’t come up with any other idea)

Help, please! Thanks for any thoughts.
usually a little led comes on when the pcb is goosed, on theboard itself
 

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