Pump runs OK on the bench, so what's the problem?

[K300]

Hi,
Ferroli 30 boiler,

symptoms are that the burner shuts down after a few minutes of starting when the central heating switches on.
There is usually a humming noise coming from the pump, which suggested to me that the pump was getting power but wasn't actually turning and was obstructed in some way.

Suspected the pump so removed it and got it on the bench.

Ran it a couple of times for probably about 30 or 40 seconds and it runs fine(and quietly) on all 3 settings.
Even with a reasonable amount of pressure being placed on the face of the impellor with the handle of a screwdriver, in fact now got a few flats on the handle.
So now I am baffled, is it possible that my method of testing is flawed and the pump is actually knackered.

Thanks in advance chaps.

Stu.

PS. I should add that I had also suspected a blocked system but while messing around with the 3 speeds and the bleed cap while it was in situ it seemed to start working and all the radiators in the house got hot. But this only lasted a short time(minutes) and it went back to the same problem. I would also have suspected the obvious thermostat on the wall but with the pump humming I presumed it was getting power. Should I check it anyway.

 

[K300]

Come on chaps,
if you don't spill the beans it means I'll be going out tomorrow and spending money and I may not have to.

 

[uselessFCUK]

Stu

Assuming this is a conventional system with F&E tank and DHW cylinder... I'd suspect motorised valve or circulation problem such as closed rad valves and no form of bypass.

So... is it this type of system or combi?

Any work been done recently?

Regards
UF

 

[ollski]

Why is the pump on a bench?, if it's receiving 240v at the live connection on the pump but not spinning when the cap is off the end it's knackered

 

[Sylvan Tieger]

Hi,
Ferroli 30 boiler,

symptoms are that the burner shuts down after a few minutes of starting when the central heating switches on.
There is usually a humming noise coming from the pump, which suggested to me that the pump was getting power but wasn't actually turning and was obstructed in some way.

Suspected the pump so removed it and got it on the bench.

Ran it a couple of times for probably about 30 or 40 seconds and it runs fine(and quietly) on all 3 settings.
Even with a reasonable amount of pressure being placed on the face of the impellor with the handle of a screwdriver, in fact now got a few flats on the handle.
So now I am baffled, is it possible that my method of testing is flawed and the pump is actually knackered.

Thanks in advance chaps.

Stu.

PS. I should add that I had also suspected a blocked system but while messing around with the 3 speeds and the bleed cap while it was in situ it seemed to start working and all the radiators in the house got hot. But this only lasted a short time(minutes) and it went back to the same problem. I would also have suspected the obvious thermostat on the wall but with the pump humming I presumed it was getting power. Should I check it anyway.

Hi Stu, do you have a flow control valve on your system?

It is a device that prevents the stratification of hot water rising when the boiler is off and the pump /circulator over comes the weight of the flow controller.

Also have you checked to make sure the circulator /pump is not air bound and (cavitation) impeller spins but because of air can not pump fluid.

 

[ChrisR]

Stu you need to measure the rpm and torque . Torque you've sort of done, , now you need a tacho, or some ingenuity with a bulb..
There could of course be blockages
anywhere...

 

[K300]

Hi chaps and thanks for all the helpful stuff.
In the end it turned out to be the air control valve venturi, does that make sense?

The part was £2.

 

[ChrisR]

Yes, if it had melted or dropped to bits! That's what they do on Ferrolis!