Radiators hot even when only HW is calling - confusing

[tpot5]

I'm really confused about what is going on here.
The symptom seems simple: hot radiators even when CH is off but HW is calling.
But this one is confusing.

I have a Y-plan system...

Boiler: Potterton Flamingo 50s (pretty old but serviced).

Pump: Katsu circulating pump (model 151711).
Mounted vertically.
On 'flow' side with flow upwards towards the diverter valve.
On lowest setting of 45W

Diverter valve: 22mm 3 port ball valve. A, A/B, B.

Diverter Actuator: Corgi A3MID-C

Controller: Horstmann Centaurplus C27 series 2

Room thermostat: Honeywell, manual, circular wheel

Standard hot water tank.

Just to confirm a few things:

The arrow on the pump is pointing upwards toward the diverter valve.
The room thermostat is working (checked the CH calling terminal with neon screwdriver)
The controller is working (checked the CH calling terminal with neon screwdriver, and the other terminals too)
In an attempt to fix this I have just replaced the diverter valve and actuator.

The problem still persists.
So I wired up the old actuator, attached to the old ball valve, in parallel with the live one.
I did this so that I could see what the new one was doing (Big assumption is that I replaced a working actuator and valve when I needn't have).

So when HW is calling and CH is not, the parallel valve is firmly closing off the CH port.
But my radiator are still hot!

I hope someone can help me.

I’m sitting back waiting for the explanation from @PigletJohn

"parallel valve is firmly closing off the CH port."

but is the new one?

feel the three pipes of the "T"

the input pipe shuld always be hot.

the HW pipe should only be hot when clling for HW

the CH pipe should only be hot when calling for CH )once hoye, they will talke half an hour to go cold).

Is the water in the feed and expansion tank hot? Is it visibly running? how deep is the water, and how deep is the layer of mud?

Some photos of the pipe layout would be useful.

Also

what sort of timer programmer have you got?

BTW

please fling your neon screwdriver in the bin, after smashing it into tiny fragments with a big hammer, and invest in a digital multimeter.

you an probably get one for around £12, perhaps in Aldi or lidl Aisle of Mystery when next in stock or Screwfix

the parallel valve is the old one but it is behaving as I would expect.

feeling the 3 pipes after about 45 mins of setting state
CH and NO HW = centre pipe very hot, CH pipe very hot, HW pipe hot-ish

from previous observations after several hours:
HW and NO CH = centre pipe very hot, CH pipe very hot, HW pipe very hot
HW and CH = centre pipe very hot, CH pipe very hot, HW pipe very hot

The expansion tank is cold, about 22cm of water with about 1mm of slime at the bottom (tested with finger).
No water is running in to the expansion tank.
The feed pipe at the top is cold, at the bottom (where it joins the return from the hot water tank) is luke warm. The luke warm runs up the feed pipe for about a meter (which is about 30cm above the heat flow in to the hot water tank)

I'm not sure how to post photos but here's a link to some...
photos.app.goo.gl/Rew4x2oVKq12RdVa6 - diverter valve
photos.app.goo.gl/KCM5vpHtZ8B6b6vt7 - flow to the tank
photos.app.goo.gl/HGf2B1oyAmEyPjVJ9 - pump to diverter valve
photos.app.goo.gl/2WQrGy4M2r7suwrv9 - timer

I have a digital multi-meter

BTW

please fling your neon screwdriver in the bin, after smashing it into tiny fragments with a big hammer, and invest in a digital multimeter.

you an probably get one for around £12, perhaps in Aldi or lidl Aisle of Mystery when next in stock or Screwfix

@PigletJohn I was a fan of yours before but even more so now! You're a legend!

Also it may help you to know that I replaced the pump about 5/6 years ago, when the old one failed completely.

But this current issue only started around the start of the cold weather last year.

Now the warmer weather and higher fuel bills are on the horizon I really want to get this sorted.

So the CH pipe is always hot.

I expect you have a mid-position valve, capable of opening port A, or port B, or both ports together. Please verify. The instructions will tell you if, with no power to the motor, the spring returns the valve to the "hot water only" position. I'm trying to think if it might be fitted with the "A" and "B" ports the wrong way round.

Have a look at the colours of the wires on the head. I think you will have pink, white, grey, blue. Can't quite remember. With your multimeter, see which ones are off with both thermostats off, and which go live with each stat and with both stats on.

If you can take the motorised head off, you can rotate the spindle manually. Try that, it will show if the ball is moving freely and correctly sealing one, or the other or neither of the ports.

It is a mid position valve.

Port A is supposed to be CH and indeed is connected to the radiator circuit.

When there is no power to the motor it stays on it's last position. But then the pump isn't running at that point.

All voltage measurements are with the parallel diverter removed:

No CH + NO HW -> orange=0V, white=0V, grey=237V
No CH + HW -> orange=238V, white=0V, grey=53V
CH + No HW -> orange=238V, white=238V, grey=238V
CH + HW -> orange=235V, white=237V, grey=61V

orange is the "heating only" output from the actuator.
The reason it shows 238V for "No CH + HW" & "CH + HW" is because the 'COLD' side of the the tank stat is pulling it up.
When I disconnect the orange wire from the terminal block it shows 0V in those conditions.

I played around with the valve spindle before I installed it to compare it with the one I had just taken off. They both appeared to work just fine.

The partial voltages on the grey wire surprised me. But as I said before, the parallel divertor appears to behave as expected in those states.

correction. when there is no power at all the valve moves to B
when there is No CH + No HW the valve stays in it's last position

I understand not a single word of this but it is amazing to read

Do you need to replace the flibertyjibbet?

Re - Room thermostat: Honeywell, manual, circular wheel

My answer might not be relevant, but it might help others….

In the factory, during manufacture, apparently they randomly stick the circular wheel on - but not to reflect the correct actual temperature.

So, you can prise the “wheel” off manually, get a couple of thermometers, check the actual ambient room temperature, then stick the “wheel” back on - but in the correct position to reflect the actual temperature.

I had the same problem with my radiators being on when I had set the thermostat to “off”

(Forgive me, when reading the OP, I though I had accidentally stumbled onto the Facebook page called “The Dull Mens Club” 🤣😂🤣)

That Facebook page is worth checking out btw…

@PigletJohn

For the moment I'm going with the hypothesis that the valve is moving in the correct direction but with not enough force because of the partial voltages.

Looking at the circuit diagram, either the "HW Off" from the controller is not droping to zero or the tank stat is not dropping to zero.
In the morning I'm going to separate the connection and test those components individually.

Please tell me if I'm barking up the wrong tree.
(or just plain barking @SynchroSwimmer :) )

diaphragm perished?

@Movingonup22

@tpot5

correction. when there is no power at all the valve moves to B when there is No CH + No HW the valve stays in it's last position

Do you mean it moves to "B" open (hot water on) with no power?

Pulled back there by the spring? That's what I was expecting.

If you rotate the spindle manually (with motor head removed) to the HW on position, does it give you HW hot, radiators cold?

If the head works as I expect, it includes a switch to turn the pump on when the head rotates with an "on" signal. Some older systems always turn HW on when CH is on, this is done by a "gravity" switch, usually on the back of the programmer. Yours should have this switch set to "pumped" not "gravity."

Btw the "elegant" way to add pictures

Under the message box it says

"Images (up to 30 a day) choose file"

This is not available to new members.

We regularly have this problem. It happens when the valve gets stuck and the hot water goes to the CH rather than the hot water tank. We have had British Gas out today to fix it.

@PigletJohn.

Yes I mean that the valve moves to open port B (HW).

The voltages you posted are what I would expect to find on a y plan system to be honest. Grey only has 240v when the hot water is off to allow the motor to drive the valve I to heating only position. A small amount of voltage can often be found on grey when hot water is on and a small amount on white when heating is off.

It sounds to me like the body of the valve is passing water to the heating circuit.

@PigletJohn

Your assumption about the Actuator is correct except it doesn't come with a switch on the back for "gravity / pumped".

Rotating the spindle manually is a very good test, it works way better than I thought it would.

So, with the radiators cold, HW calling and CH not calling I rotated the spindle and it gets sucked in to closing the CH valve (I was expecting to have to hold it there).
The fact that it gets sucked / pushed into that position verifies that the pump is pumping in the correct direction (no matter how unlikely I did wonder about that).

After a few minutes the radiators were at high temperature.

So with this one test we have proved a problem that is independent of the actuator, thermostats and controller! Nice.

But it doesn't solve the problem.

(BTW my wife tells me that she turns off all of the TRVs in the summer. So maybe that's why I didn't notice this before.)

I'm trying to trace the pipework now, including the connections to the Boiler.
I'm having trouble finding a manual for the Potterton Flamingo 50S. There's an RS50S but I assume that it won't necessarily resemble the 50S.

Thanks for your help so far.

Forget the boiler as there is one switched live and the boiler doesn't know if it is being called for heating or hot water. The brass body of the valve is passing water to the heating circuit when the hot water is on. You need to drain the system and replace the three port valve or pay for so done to do it for you.