Boiler lights, runs for 2-3 mins, shuts down for half an hour.

[PeterMcC]

Hi

I've an Ideal Concord CX60, open system, radiators and water heating - both pump fed.

Pilot light stays on, 3-port valve functioning, external thermostat on wall functioning, pump running (spindle is certainly turning).

Switch boiler on and it runs for 2 or 3 minutes then it shuts down; eventually it will come back on and repeat the cycle...

Problem arose Friday afternoon during normal operation when I noticed that the heating had gone off.

Thoughts:

Is it the thermostat in the heat-exchanger water-jacket that has developed a sudden over-sensitivity? Is the pump not really pumping and so the heat's not being shifted away from the boiler and the boiler 'stat is shutting down?

Other than that, I've run out of ideas.

Any suggestions gratefully received.

[PeterMcC]

Just to clarify - that thermostat is external to the boiler, it's on an internal wall in the house and is the main sensor/adjustment for controlling ambient temperatures.

[John Stumbles]

Is the flow pipe out of the boiler getting as hot as the boiler thermostat setting would suggest (e.g. scalding at max)?

If the boiler's getting the water as hot as expected but the heat isn't getting away from the boiler then it will cycle like this. If you had a Y-line strainer in the system I'd suspect that it's blocked.

[PeterMcC]

Seems to be.

That's where my thoughts are heading.

A Y-line strainer, eh?

Got me beat there. I assisted in the installation but don't recall anything about strainers. I'd assume (Oh dear, here comes trouble) that the strainer ought to be accessible for cleaning. Since I have never seen anything on the system that might be the unexplained presence of said strainer, I'm guessing that there isn't one.

There's hot water getting past the pump - pipes hot on all three ports to the 3-port valve, but it's only just warming the feed pipe on the nearest radiator. Were it not for the fact that the spindle's turning in the pump, I'd say that the pump had failed.

Is there a scenario in which the pump still spins but fails to drive a sufficient rate of water? My experience of central heating pumps has been that they spin and work or don't spin and don't work - I'd always assumed (here we go again) that there was so little in them to go wrong that there wasn't a "working a little bit" status.

...and my thanks for your reply, John.

[PeterMcC]

PeterMcC wrote in

I've split the pump body from its fitting and find that the impeller disk is spinning freely on the end of the pump spindle. I guess it's possible for there to be a clutch system but...

...can anyone confirm that the impeller should be fixed to the spindle without the capacity for rotational movement independent of the spindle?

-- PeterMcC If you feel that any of the above is incorrect, inappropriate or offensive in any way, please ignore it and accept my apologies.

[Andrew Gabriel]

Some old pumps used to have a magnetic link between the impeller and the rotor which provided both a waterproof seal and jammed impeller protection, but I don't think modern ones have worked that way for quite a while.

[The Natural Philosopher]

Yes, but its a known failure mode. On car water pumps as well.

Often enough its just a push interference fit.

Corrosion can etch the fit till it simply goes free running. Once that happens it stays that way.

[PeterMcC]

Andrew Gabriel wrote in

Thanks - as I suspected.

So, it's a cold weekend 'til the plumbers' merchants open on Monday - just knowing that my wife is visiting our daughter in 35 degree Oz will keep me warm...

...perhaps?

[PeterMcC]

The Natural Philosopher wrote in

Many thanks for the reply - I guess I can stop waiting for the one that says, "Oh, easy! Just press the little button that you'll find beneath the impeller - that'll fix it."

[Andrew Gabriel]

You can get pumps at places like B&Q. You may be paying a premium though, dunno.

[PeterMcC]

Andrew Gabriel wrote in

Thanks for the suggestion - unfortunately it's a bigger than standard pump and they don't stock them :(

[Phil B]

Peter,

At the end of the pump in the middle of the big cylindrical bit is a big screw about 1/2 inch across which has 2 functions - it's a bleed screw and also gives access to the end of the spindle.

1. Turn pump off. Remove the big screw. Hopefully the spindle inside has a hole in the middle. Insert a small screwdriver in and check that it will turn. I had one which was stuck and this freed it. Replace screw.

1. I had a frustrating session a few tears ago after draining and refilling my system, caused by an airlock at the pump which was very stubborn to remove. Turn boiler off if you can. Run the pump. Loosen the big screw slightly - a few drops of water may escape but if you also find that air fizzles out then leave it like this until the fizzling stops. Tighten up, turn boiler on and away you go.

Good luck. Phil

[John Stumbles]

Ah - that's it! Never come across that one before. That'll teach me to read other posts before blathering away about airlocks & so on (though they have happened in my experience too).

[PeterMcC]

John Stumbles wrote in

Impeller detached from pump shaft, new pump fitted, I'm warm.

Many thanks, John, and to all who replied.

The kindness of strangers...

[The Natural Philosopher]

Lucky you. Ive got a jury rigged piece of live wire bridging the place where by supposed-to-have-been-dispatched-last-week effing sunvic radiostat should fit.

11C in the living room was pushing teh boundaries of eco freindlisness a shade TOO far.

It will take about 24 hours running flat out anyway to get up to temp.