How to test central heating pump?

[Sam Wain]

Happy New Year everyone!

I need a little help on figuring out what's wrong with my central heating (CH) system. I'm in a new house, and I know the system has a single motorised diverter valve for hot water and radiators (rads). Problem is almost none of my rads get hot, except for 2 or 3 that get warm to touch, but not hot.

I first thought it might be sludge, so need a power flush; but I'm thinking the pump is not strong enough.

I know that the boiler fires and provides hot water into the CH pump. I have tried to ensure the pump is not jammed by manually turning the 'axle' with screwdriver/spanner. I think the diverter valve may also be jammed, but it's stuck to supply rads only (fine for now).

How do I test that the CH pump is working to specification? How can a test for low ouput pressure? Can I do this with simple tools at home? Is there a way that I can tell if the impeller is damaged with the pump in place?

In Photo 2, you can see the CH pump electrics are coming away. If these were restored would the pump function normally?

If I need to change the CH pump for a new one, how do I select the right one to buy (to provide right pressure for my CH system)?

In Photos 3 and 4, you can see the issues with input and output isolation valves. Are these damaged? If I change the pump, do I need to change these valves too?

Photos:
1. CH pump: 20221221-235335 - https://ibb.co/JcN2XRf
2. CH pump: 20230102-224718 - https://ibb.co/FDbbWzg (electrics coming away)
3. CH pump input: 20230102-224646 - https://ibb.co/0Q9QH4y
4. CH pump output: 20230102-224631 - https://ibb.co/F6h33Zg

 

[gmartine]

It doesn't look great but that doesn't mean it's faulty.
Is the pump switched to it's highest setting? You can test the pump "manually" by trying to arrest the pump spindle speed with your screwdriver. You shouldn't be able to.

 

[Sam Wain]

It doesn't look great but that doesn't mean it's faulty.
Is the pump switched to it's highest setting? You can test the pump "manually" by trying to arrest the pump spindle speed with your screwdriver. You shouldn't be able to.

I agree - just because it looks bad, doesn't mean it's not working.

The CH pump is set to '3', which is believe is its highest setting. Photo 1 (OP) shows that's the most powerful speed.

The CH pump spindle has a bolt at one end, so I need to use a spanner to arrest it. How do I go about doing this? Do I expose the spindle, locate it in the impeller and then go and start the CH? Should I expect to see the exposed spindle spin? Do I hold the spanner in place on the spindle and then turn on the CH?

 

[Last Plumber]

You could test the capacitor on that but you will need a suitable meter.
Don't get involved with it if you are not competent. Anything electrical can be dangerous if you aren't experienced. Even when isolated from the supply, capacitors can be nasty.

 

[ShaunCorbs]

Jam a screwdriver into the impella with light force see if it stops if it dies it’s dead

 

[Deleted member 120897]

How do you know the 3 port is jammed? It it is jammed, the it sounds likely you be the pump.

 

[Sam Wain]

Thanks everyone for the advice so far.

I got the CH pump changed out. My old one had stopped reliably starting when turning up the room thermostat. New one runs, and is pumping hot water round the rads.

I still have the problem that almost none of my rads get hot, except for 2 or 3 that get warm to touch, but not hot. And I'm 99% certain the diverter valve is jammed directing water to rads, as the pipe into the hot water tank is cold to touch.

The guy I got in to change out the CH pump tried to investigate, and said that there's no return flow back into the boiler. I'm not sure how he checked this, but he observed water flow from the drain valve. He then said it's likely that there's a blockage in one or more pipes.

I tried the CH just now, and I find that rads physically nearest to the CH pump do heat up (top half only), and rads furthest from the CH pump stay cold. To me, this is contrary to a blockage - no?

What's the process to locate a blockage in the pipes? Is it possible that I need to balance the system?