Thermo syphon?

[Dave Plowman (News]

Pal has pretty ancient heating system.

Says this fault is new.

Boiler is BE and conventional flue located in the kitchen.

Hot water cylinder, pump and three port valve all in a cupboard off the

1st floor bathroom. Plumbing to all that looks a mess - despite it being done on a new build. The house is pretty well insulated hence there not being the need to upgrade the boiler as running costs are low.

But recently, he says, running hot water only, the rads on the 1st floor get warm. But the heating side pipe from the 3 way valve merely room temperature. So can someone describe how this is happening?

[SH]

either the pump has failed or there is no power being fed to the pump..

what you are seeing is thermosyphoning where hot water rises and cold water sinks....

(you did say boiler is on the ground floor, the HW cylinder is upstairs and only the upstairs radiators are getting warm.)

[Dave Plowman (News]

The pump is working normally, as it is needed to heat the water cylinder. Which is working OK.

But why suddenly?

[Brian]

Check the Three Way valve isn’t sticking. You can usually move the lever manually which, sometimes, frees them. Also check the pump. It is always worth bleeding the system, especially when the heating has been sitting idle. If there isn’t inhibitor in the system the other rads may be have ‘air’ in them which is why only the upper ones are hot. ( While ‘air’ sometimes collects in the higher rads, depending on the pipe runs, this isn’t always the case. )

[Fredxx]

That is my experience, except I have known the "ball" in a 2-port valve to become marked from being in one position for a prolonged duration, like the summer period. And so when moved allowed a weep of water past the seat.

Sounds like a new valve to me.

[Andrew]

It's not unknown for the paddle or whatever the diverter is, to disintegrate.

[Roger Mills]

Indeed. But if the valve were faulty, surely its heating outlet pipe would be hot - but apparently, it isn't.

Do we know whether the valve is in the flow or return side of the primary circuit? The explanation for the problem may be different depending on the answer to that.

[Brian Gaff]

Yes I'd have thought if it were an actual blockage or air it would have grumbled and given up by now. Brian

[Dave Plowman (News]

Quite.

I'm not sure. Except it is on the same circuit as the pump - and is connected to the higher of the two coil connections on the cylinder.