Central heating pump not running - how to test?

[Craggo]

Hi all,
This morning my boiler locked out with F22 (dry) and keeps locking out when reset for both HW and CH. I suspect it may be the pump as I cant hear it running anymore when the programmer switches on. The boiler still fires up but faults on F22. How can I check the pump and might it be something else?

Boiler
British gas 330+ (new heat exchange and flue installed two weeks ago by vaillant)
System
open with HW tank, 3 way valve and pump etc, I've bled the rads, and bleed valves near pump / 3 way valve (lots of air this morning)
3 way valve
replaced 5months ago, the programmer still moves the selector to H or W and boiler fires up
Pump
British gas multihead g (grundfos), have unscrewed bleed valve and motor can turn.

thanks for your help

 

[stem]

I normally remove the big silver vent screw that exposes the pump shaft to see if it is spinning when it should be. If it's not, the end of the pump shaft has a slot in so it can be manually turned with a screwdriver, this will show if it is free to move or not. Some water will come out when you remove the vent screw, so I do it when the system is cold and have something ready to catch or soak up the water.

If the shaft is not spinning when it should be, then I would check the wiring terminals of the pump with a multimeter to see if there is 230V present between its L & N terminals which will show if it is receiving power as it should be or not. If it is receiving power and not operating, there is a problem with the pump. If there is no power the fault is elsewhere.

 

[Craggo]

Thanks Stem,
The pump is free to turn, ill check the power to the pump tonight.

 

[durhamplumber]

Thanks Stem,
The pump is free to turn, ill check the power to the pump tonight.

Most common fault,,3 way valve,,even if replaced 5 months ago.Did they replace whole valve,or just motorised head?

 

[stem]

The three port valve always has at least one open port, so it wouldn't stop water circulation through the boiler provided that the pump was running. If the microswitch inside the valve that makes the orange wire live when only heating is required had failed, the boiler wouldn't be firing.

I'm not too familiar with BG re-badged products, but I think your boiler will be wired as below, and if so, the boiler is responsible for controlling the pump, and the pump is wired directly to it. When the boiler runs, so should the pump and it should continue to run for a short time after the boiler goes off.

So, if the boiler is running, thus showing it is getting power from the controls / motorised valve etc, and the pump isn't running; then either the boiler's control of the pump, the pump itself, or the wiring between the two has failed. When you check the power supply to the pump that will give you a pointer.

Fault code 22 doesn't only indicate a problem with the pump, but as you suspect it, it's a good place to start.

 

[Craggo]

The 3 valve head and body was replaced, this cured the problem of the boiler and pump not firing up or only the HW working (the motorised valve was replaced to start with but didn't cure the problem completely so a new valve body and head was installed).

ill see how I get on tonight - thanks for your help

 

[Craggo]

Checked the terminals for the pump at the wiring centre and there's no power being supplied to the pump when the boiler is firing up (either in HW or CH). There's 230v coming into the wiring centre, continuity between wiring centre and pump and when I tested the contacts on the pump I was getting 230ohm.​

The 330+ boiler is a glowworm and has a similar diagram to Stem's post
The boiler is on a different floor to the pump / wiring centre so I'm not sure how to test for continuity in the wire between the two, how would I do this?
Any other ideas?
Thanks

 

[mattylad]

You can disconnect both ends then join them together at one end (join L&N at pump end) HOWEVER - only do this if you are 100% certain that the pump supply is disconnected from the source.
If you get continuity through both L & N at the non joined end then you have continuity.

When you have finished testing, rewire them, starting at the pump end.

 

[Craggo]

Ahhaa!
Brilliant - thanks

 

[stem]

Checked the terminals for the pump at the wiring centre and there's no power being supplied to the pump.

There's 230v coming into the wiring centre

Isn't that contradictory? Either there is 230V to the pump or there isn't.

Unless by that you have tested other terminals at the wiring centre that aren't pump related. But I don't understand why you would do that. The pump should only be connected to the boiler and nothing else, what is connected to the other terminals is irrelevant.​

 

[Craggo]

Hi Stem,

I tested the wiring centre pump terminals - no power. I then tested the incoming power terminals in the wiring centre and there's power (if nothing else to make sure my meter was working)

 

[Craggo]

I couldn't test the other end of the cable as mattylad suggested as its within a plastic cartridge in the boiler - I thought best left alone. I've called vaillant back to see what they say.

thanks for your help

 

[durhamplumber]

I couldn't test the other end of the cable as mattylad suggested as its within a plastic cartridge in the boiler - I thought best left alone. I've called vaillant back to see what they say.

thanks for your help

At least you had a go and did not have any diy disasters.

 

[stem]

OK understood, the 230V has nothing to do with the pump then.

there's no power being supplied to the pump when the boiler is firing up (either in HW or CH).

In which case, it would be unusual for wiring between the boiler and pump to physically fail, but it could happen especially if it goes via a junction box or wiring centre; but is rare if nothing has been disturbed. Most likely the boiler control / PCB isn't switching the pump on when it should be. Anyway it's a simple test for a Vaillant engineer, he can check to see if there is 230v at the boilers pump terminals.

 

[durhamplumber]

OK understood, the 230V has nothing to do with the pump then.


In which case, it would be unusual for wiring between the boiler and pump to physically fail, but it could happen especially if it goes via a junction box or wiring centre; but is rare if nothing has been disturbed. Most likely the boiler control / PCB isn't switching the pump on when it should be. Anyway it's a simple test for a Vaillant engineer, he can check to see if there is 230v at the boilers pump terminals.

Why can you not wire the pump directly to the mains to test