How to diagnose my Central Heating fault? Pump not running

[25th QV]

Basics.

Gravity system
3 wire control (for some reason I'll never fathom)
Tempus Timer
Bosch Greenstar Boiler (about 6 years old)
Grundfos UPS2 15-50/60 pump (also 6 years old)

Status.

Power to boiler
Boiler fires up, then after a short period, rests again as water is not flowing through
Timer set to on (tested constant, timed and manual setting)
Room stat appears functional and 'clicks' to call for heating when appropriate
Light on pump on
Pump silent - no hum, no vibration, nothing
Removed front access port and manually rotated impeller with a screw driver - turned smoothly and freely
Radiators cold, no hot water
Heating has not been switched off for any period as we use it daily for hot water, so never sat idle more than about 12 hours

My own basic understanding is that either the pump is broken, despite receiving power which given the impeller rotates is likely electric (capacitor blown?), or despite all indications, power is not being called for regardless of indications on thermostat or controller?

Any ideas how I might perform some diagnostics to help identify the problem? Do I pull the pump wiring from the junction box in the airing cupboard and try to add mains directly to the pump?

Any ideas or suggestions welcome.

[guywilko]

If you need a new pump, I would recommend Wilo pumps. The Yonos Pico allows very precise power setting, runs super quiet, is easy to swap and has multi modes.

[Brinyan]

You said that the light on the pump is on, when the programmer, stat etc are calling for heat, so the pump has power.
All the symptoms lead to the pump needing replacement.

[.:ian:.]

The pump has some speed controlling electronics, its reasonably likely this is the fault.
It might work on a different speed.
The only other thing that can fail are the pump windings, if you take the control box off you can test the continuity.

No idea if you can get just the speed controller, maybe on ebay.

There are certainly a lot of grundfoss pumps on there. Seems like every plumber just punts them off on ebay after replacing them.

[GAjon]

Three way valve!

[Rough101]

If there is only live neutral and earth at the pump, and they’re live but it’s not turning, it’s failed.

Some have a permanent live then a low voltage trigger circuit though.

What colour is the lamp? I’m sure these can show a drive error, perhaps by the lamp displaying amber rather than green. Albeit there a million configurations of UP.

Edited by Rough101 on Sunday 22 September 09:11

[Xcore]

Pumps proven to have power but is not running…I’d say that’s your issue.

[25th QV]

Thanks all, after some more digging, the pump is switched live only - L,N,E feed. If the light is on, the pump should run so I've pulled it this morning and ordered a new one - or at least the latest equivalent model.

PH Experts to the rescue once more - thanks chaps.

If I can return the favour to anyone by sharing my own expertise, please contact me directly.

My specific areas of brilliance are, in no particular order:

Cross-threading splines
Wet sanding through clear coat
Over-tightening self tappers
Drilling holes at an angle
Measuring 3 times and still cutting wrong
Snapping drill bits
Tearing belt sanders
Cutting through grinder cables
Rounding screw heads
Testing glue joint strength too early
Bluntening chisels then re-grinding them worse

Happy to help.

[Rough101]

25th QV said:

Thanks all, after some more digging, the pump is switched live only - L,N,E feed. If the light is on, the pump should run so I've pulled it this morning and ordered a new one - or at least the latest equivalent model.

PH Experts to the rescue once more - thanks chaps.

If I can return the favour to anyone by sharing my own expertise, please contact me directly.

My specific areas of brilliance are, in no particular order:

Cross-threading splines
Wet sanding through clear coat
Over-tightening self tappers
Drilling holes at an angle
Measuring 3 times and still cutting wrong
Snapping drill bits
Tearing belt sanders
Cutting through grinder cables
Rounding screw heads
Testing glue joint strength too early
Bluntening chisels then re-grinding them worse

Happy to help.

There is a procedure on these pumps to to vent them, then set them up, mind follow the stages to make sure that it works properly. As much energy as these little variable speed pumps save, a lot end up in landfill prematurely.

[essayer]

Make sure you have a big wrench to undo it

[25th QV]

essayer said:

Make sure you have a big wrench to undo it

The size and range of my spanners inversely matches my skills and ability - "all the gear......"

To be fair, the union nuts yielded with very little effort as everything is pretty new and nothing had corroded or seized. Even the rubber seals were in nice condition (will replace, obs).

Edited by 25th QV on Sunday 22 September 10:57

[miroku1]

You dont need to undo the large nuts on the pump union you can undo the allen bolts and swap the head only

[speedyman]

Id connect the new pump before removing the old one and test to make sure it's really the pump that's at fault. Running the new pump for a few seconds dry won't harm it.

[Murph7355]

GAjon said:

Three way valve!

I was going to say this.

If the new pump doesn't work, that's the next step IME