Odd Central heating issue

bob_a_builder

Pretty standard set up cond boiler, pump, HW tank, honeywell Y valve etc

Had a couple of showers this morning, hear boiler running as expected.

But notice rad in landing is hot, in fact all upstairs rads are hot, check downstairs ones, but no heat in those
CH stat set to 18, so not expecting any CH

Waited till all cooled down again, made sure room stat was at min, turned HW tank stat to max

Same thing all, upstairs rads hot, but cold downstairs

Y Valve would either be HW or CH or mix - so why are only upstairs rad getting hot ?

missbiggles1

Did you intend to put the central heating on?

bob_a_builder

No
and no setting have been changed for a while

On the time clock both CH and HW are set to come on @ 06:00 and off @ 22:30

But I control CH from prog room stat which in summer is set to low temp - 18 ish

plus in my test I set room stat to min to ensure no heating requested

ariba10

Sounds like a Diverter Valve problem.

Not the end of the world job.

Any reasonable Plumber should be able to sort it out.

bob_a_builder

Its the logical culprit
But why only upper rads heating ?

Heedtheadvice

Best suggestion I could give for that apparent disparity is that the Y valve is just 'leaking' a small amount so low flow through the ch rads system. If the flow fed the upstairs first then given the warm weather they would get quite hot owing to just low losses of heat......and if that was the case then eventually downstairs should get hot too. How long does it take? Are all rads equally hot? Is the hw feed pumped -presumably it is like the ch-but symptoms would seem to fit gravity circulation better! Maybe just a red herring!! Do you have TRVs on downstairs rads?

Can you get at the valve as they usually have a manual control lever too? You can operate that lever to all positions to see what the result is. You could also switch off electricity power and remove the head control box (probably depending upon design) and even use pliers to see if the valve is moving fully. Recently experienced similar problem with diverter valve sticking physically and some rads getting hot on the hw only demand. It was a small amount t of rotation but the pliers gave enough grip to force compete movement showing it was a physical problem.
If valve is physically OK then may be a motor, switch or other electrical issue. Often the control head can be replaced separately to main valve body.

Le_Kirk

I had this exact problem a while back and it was indeed the 3-port or Y valve. One of the pillars that hold the spring had snapped and so the valve was not being held closed allowing a weep of water to pass. I did a temporary repair using sticky back plastic and a fairy liquid bottle (actually I removed the pillar and replaced it with a bolt through a newly drilled hole in the bottom plate) until I could obtain a replacement valve head. I noted that the design had changed and it is now a steel pillar.

bob_a_builder

Ok - thanks for those suggestions

Once I've cleared the airing cupboard to get to the valve, I'll be trying those

bob_a_builder

Turns out I've got the old type honeywell valve, ( 4 screw rather than 2 ) where taking the head off allows the water to come out, which it did, so quickly screwed it back - leaking stopped fortunately.

Makes it difficult to check the valve on its own

So looks like it'll be a new valve

southcoastrgi

Set the timer so it's only calling for hot water then feel the pipe on the valve going to the heating, if it starts getting hot then it's prob the valve