dead central heating pump or something else??

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Hi.
I have a conventional heating set-up, with a honeywell 3-way valve (V4073A) and a hot water cylinder.
The last few days we've been short of hot water, and now it's packed up.

When the timer calls for hot water, the boiler fires, the pump runs and the pipe between the 3-way valve and the cylinder gradually gets hot. The boiler only runs for a few seconds though before it stops, presumably on temperature. The 'delivery' side of the boiler is red hot, but the return is cold.

I've taken the nut out of the back of the pump and some black water campe out and the spindle is turning.

The outlet pipework from the tank cylinder loop however never gets warm. There is a 22mm gate valve on the outlet which appears to move freely.

The upstairs rads seem to beed ok, and if I run the system with heating on, the heating delivery pipework gets hot, but it seems to take a long time to see any warmth in the pipework to any rads. When i've checked the boiler again, it's still not running, presumably because the hot water's just not getting away from it...(??)

Is it possible that the pump is turning but not pumping anything?? can the impeller become disconnected from the spindle? It's a 3-speed Grundfos pump on it's highest setting.

Any suggestions?

Thank you in advance
 
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1:-If you know how, check that there is 230v at the pump.2:- Remove the chrome screw at the front and insert a thin screwdriver and engage the shaft to see if it is turning.(you should be able to hear the motor running) If you prove power to the pump and its not spinning then its a new pump needed.
The impeller can become detached or clogged with crud which would prevent circulation. The only way to check that is to remove the pump head and look.
I hope your pump valves hold.
 
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yep, there's power to the pump, and i've already had the screw out of the back and it's not siezed, and the spindle is turning.

Can the impellor become detached from the spindle?
 
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Is the pipework going in and coming out of the pump hot when the boiler is working?

If not then its the pump that is faulty.

Andy
 
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Yep, pipework in and out hot, but the out is not rapidly hot. It's difficult to tell as there's not much room between the pump and the three way valve. after the three way valve there's definately not much flow.

i've followed tom's top tips on youtube, and there didn't seem to be much wrong.

That said, having flushed the impellor under the tap (despite it looking pretty clean already, the system seems to be working again! - still none the wiser as to what the issue was.

The impeller was black, and sort of chalky to touch. Is that right? or does that mean the impellor is partially fouled?

Thank you all for your assistance.
 
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Pull the lever on the 3 port valve and latch it open and turn up your room thermostat, (Wait approx. 30 mins) do all the rads get hot.

Andy
 
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Is the hot water HOT?

Also are there any bleed valves in the cupboard next to the cylinder? If so bleed them with the heating and hot water turned off.

If everything is bleed and rads and hot water is hot then that means you have fixed it.

Happy Days.

Andy
 
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talking of bleed valves, there is a braukmann ea122a automatic air vent on the pipe between the three-way valve and the cylinder, and this was set to 'closed'. I turned it to 'open' and some air was released. Presumably this vent should be left in the 'open' position?

This is the only vent close to the cylinder, except for the normal expansion vents etc.
 

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