please help, odd problem with heating...

[iany]

Hi,

This seems similar to other issues but not the same, its down to water and CH, CH will only come on if water goes on first, but then will stay on if you turn the hot water off after.

So if you do "hot water on, heating on" both work and valve goes to mid position.

then turn off hot water and valve goes to CH position. CH then runs fine.

turn off all and valve goes back to start position (HW only)

turn on HW and it stays in first position and works.

so if the timer is set to turn on both half the time it doesn't start the heating, you have to manually turn HW on first...

One thing i noticed is that you can here a relay click in the programmer if you turn HW on off, if HW if already off and you toggle CH it doesn't click....

I've changed out the 3 way valve head yesterday, its a drayton MA1.

system is a vented type, boiler is quite old but appears to be in good condition, has been serviced last year.

 

[stem]

Part of the way a three port valve works, is that it utilises a 'hot water not required' signal. This is what drives the valve from it's mid position to central heating only. The wire is usually coloured grey.

This 'hot water not required' signal comes from two places. When the programmer is set to hot water 'on' but the water is hot and the cylinder thermostat is satisfied, the cylinder thermostat energises the 'hot water not required' wire via a changeover contact. This wire is also energised when the programmer turns the hot water off via a wiring terminal inside the programmer called 'hot water off'

If I have understood your described symptoms correctly, I believe that the 'hot water not required' signal is not be being provided by your programmer when the hot water is off. When hot water is switched on, it is then provided via the cylinder thermostat and so it works.

If you have a multimeter and are able to use it safely, you can check to see if the hot water not required signal is present at the motorised valve when the fault conditions are present.

But first a couple of questions.

1, Has the system ever worked properly?

2, Has anything been changed recently, other than the valve head, and did that alter any of the symptoms, or are things exactly as they were before you changed it.

 

[iany]

Hi Stem,

it has worked previously as i remember this issue has just been happening over the last month or so, when we moved in around 4 years ago we swapped the 3 way valve as it was giving hot water and heating even when just the water was on.

later on we swapped the programmer to one that had more feature on the timer, this didn't cause any issues.

i've got a fluke multi meter, so if i test with a meter am i looking for 240volts? and where can i put the other end of the meter to make the circuit if i have the live on the wire you suggested?

 

[stem]

Measure at the point where the motorised valve fly lead is terminated. There should be 230v present between the grey wire (L) and the blue wire (N) whenever the following conditions are met.

1. The hot water is selected 'off' at the programmer.

2, Hot water is selected 'on' at the programmer and the cylinder thermostat is satisfied.

Ideally you need to do this when the fault is present, otherwise it doesn't prove anything.

 

[iany]

had a further mess around since last reply...

if i start with neither on, then turn on CH, nothing happens, 3 way stays in position A (HW)

If i then -

1. turn the HW on vavle goes to mid and both work

OR

2. with HW still off manually move the 3 way to mid position, it comes to life and moves to the C position (CH only) and CH works.

so it seems that without the 3 way getting to B it never kicks the heating in.

odd isnt it?? does this info help?

 

[stem]

I think it fits in with my theory, the internals of the three port valve are quite complex, but the basic theory is.

When at rest the valve sits at the hot water only position where it's held by a spring.

When you turn on just the central heating there will be a live on the grey wire (because hot water is not required) and also the white wire (central heating required) The combination of these winds the valve fully across to the central heating only position.

When there is hot water and central heating required, the grey wire is de-energised (white remains live) and the valve is held in the centre position.

Under certain conditions, the valve can stay powered and at central heating only, even when everything has gone off, which is a drawback with the design.

The easiest way is to fault find it, is to check if it is getting the correct signals from the controls.

 

[iany]

I think (not certain until i test it) that i may have found the issue...

I tried looking for the "hot not required voltage" and found it was as it should be using NW switched on and thermostat on tank to test all 3 outcomes.


i then took the top of the 3 way and when i put it back id locked it in the mid position using the lever (as per the fitting instructions that i hadnt noticed in the box!!)... now it appears to be working ok with heating on and water off... need to start from all off and test the theory but i'm thinking i may have confused things the way i'd first put it on??

 

[iany]

scratch that it ran for a bit then went off.

drawing board again....

 

[stem]

I thought that might happen, because that wouldn't explain why the original valve head that you replaced was manifesting identical problems.

 

[iany]

Its on timed now with HW and CH due to come on first thing in the morning, will see what happens, working from home tomorrow so can have a play around and see if i can narrow down the cause.

i've found a couple of diagrams which i assume are for my type, on this link, Y type i assume?

http://www.gasboilerforums.com/wiringdiagrams.html

 

[stem]

Yes that looks about right. You can find a useful link by clicking here. Under the Y Plan heading, you can select different permutations and it shows in an animated form what wires are energised under the various conditions.

 

[iany]

that's very useful thanks

this morning both came on as per the timer, they're off now, when i get a second i'm going to get the meter and see what's going on when i want just heating only as that seems to be the issue, the odd thing is that it works when HW is also on but not separately, hopefully i'll be able to find the issue using that diagram...

 

[stem]

Please post back how you get on. It may help someone else in the future who may have a similar problem.

 

[iany]

so some progress thanks to those diagrams!

heating on only and there's no power to 2 out of 3 of the feeds expected, these being the one from the room stat to the valve and the one that goes from valve to boiler.

if i put the heating on the room stat gets power (only 24 volts is that right??) but then it all obviously works.

when i turn on heating on the timer it doesnt "click" where as HW does, i get a feeling a relay/switch inside the box might be busted??

sound about right?

 

[stem]

OK then, lets start at the beginning.

heating on only and there's no power to 2 out of 3 of the feeds expected, these being the one from the room stat to the valve and the one that goes from valve to boiler.

If I understand you correctly, there is no power to the white wire at the valve when the programmer is at CH only 'on' and the room thermostat is calling for heat. If so you need to find out why. The live starts at the CH 'on' terminal at the programmer goes through the room thermostat, and then to the 3 port valve white wire.

Don't worry about the orange wire to the boiler at this stage, that won't be live, unless both the white and grey wires are live. [It's not actually a feed to the 3 port valve, this is the live that goes from the 3 port valve to the boiler to turn it 'on' in heating only mode]

So it is possible that

When i turn on heating on the timer it doesnt "click" where as HW does, i get a feeling a relay/switch inside the box might be busted??

Unfortunately, that doesn't explain

So if you do "hot water on, heating on" both work and valve goes to mid position.

Because the white wire needs to be live for that to happen.