Cold radiators again

[Crewood]

A few months ago I posted because one or two radiators on my systems never got warm, many helpful replies told me how to get the system balanced and this cured the problem.

Now it's happened again but this time most of the radiators are cold but the hot water from the taps is almost boiling. It's normally the other way round. The pump is very hot to the touch as well.

I have a solid fuel Parkray Chiltern fire and boiler unit, could the system need balancing again or is it possibly something else this time.

Any help would be most welcome as it's turning very cold.

CC

[Wingedcat]

Sounds like either (a) one of your 2-way zone valves has stuck, or (b) your 3-way mid position valve has stuck. Try moving the manual lever on the valve to open up the CH circuit to prove this.

[Jerry]

Is the pump spinning? Sometimes they stick after the summer idle period and the heat comes from the electric power being dissipated in the windings that would normally be taken away by the flowing water. Is the inlet pipe hot all the way back to the boiler? If it's not spinning you may (depending on the design) be able to switch of the power and close the isolator valves, unscrew the bleed screw that should be at the top of the pumping chamber, insert a small screwdriver and wiggle it to turn the rotor. Then turn on the power and see if it spins. Once it's away that'll probably cure the problem. Don't forget to replace the bleed screw and open the isolator valves. Long term solution to this is to flush and clean the system and add inhibitor, alternatively spin the pump once a week during the summer.

Jerry

[Set Square]

Is it a gravity hot water and pumped central heating system. If so, it sounds like the pump has seized. If it's a gravity system, the HW doesn't use the pump, and won't be affected.

Take the end cap off the pump and see whether it is rotating. If not, turn it off, and try to free it with a screwdriver. (There should be a slot for the purpose in the end of the shaft). If that doesn't work, you'll need a new pump.

If, against the odds, it's a fully pumped system, come back and tell us what zone valves, stats, etc. you've got - and we'll think again!

[Crewood]

The pump in the system appears to be spinning, I can feel vibration, but the body is almost to hot to touch. All the pipes around the pump and those coming from the boiler are hot.

The pump is marked as a Commodore 130 with a small black box on the top that has a switch with 0 to 5 settings, the current setting is 2. I don't see where I can check if it is actually spinning or see a bleed screw. It has also run throughout the summer months.

The system has an hot water tank upstairs and a cold water tank in the loft.

One radiator downstairs is getting quite warm as well as one upstairs, the others are at best just above cold to the touch.

Anymore information I can add please let me know.

CC

[Owain]

The pump motor might be working but the impeller not.

It is quite normal for one rad to be put on the hot water loop - usually the bathroom towel rail.

There will be some gravity circulation on the heating loop which is why your other rads are getting a bit warm eventually.

It's almost certainly the pump on the heating circuit. On a solid fule installation there wouldn't normally be a pump on the hot water circuit as the boiler *has* to be able to dump heat somewhere.

Owain

[Set Square]

I would still suspect the pump. I can't remember exactly what a Commodore looks like - although I did have one many years ago. Many pumps have a cover - about 1/2" in diameter, with a screwdriver slot - at the opposite end of the pump body from the water connections. When that is removed, you can see the end of the shaft. Maybe yours is not like that?

Does your pump have isolation valves either side? If so, you could close those, and remove the pump without having to drain down. You could then wire it up to a 13A plug and see whether it's rotating - since you should be able to see the impeller. [Don't run it dry for more than a few seconds, though - it won't like it!]

Might be an idea to get one of these

as a spare, anyway.

[Jerry]

It so happens I have the same type. It's blue, right?

The bleed screw is not easy to spot as it'll be painted to match the body, but it's in the centre on the top side.

This type of pump has a fixed motor winding, isolated from the water by a stainless steel membrane, the impeller is magnetically coupled.

I suggest turning off to let everything get cold, then turn on and you should feel the pipe on the inlet side get warm as the water heats, BUT if the impeller has stuck there will be no circulation, so no heat.

It is normal for these pumps to be on the return to the boiler so the outlet side goes to the boiler for reheating.

Can you close the isolation valves?

If you cannot budge the impeller with a screwdriver through the bleed hole, then it is possible to remove the impeller side of the pump - 4 screws I recall. Lift it off, clean it up, reassemble. Be careful not to damage the o-ring seal between the membrane and the impeller body.

Jerry