3-way valve problem?

[Slaydeuk]

I appear to be having the same problem I had about 9 months ago. At that time the boiler would be dead, but would fire up when I switched the power off and on again. I decided at that time to wait until it happened again and I would then have a look at the 3-way valve and try and diagnose the problem, which I was pretty sure was in the 3-way valve. I wanted to avoid having to replace the whole unit if it was a component the was replaceable. Sods law, it didn't happen again - until today. I have just found the boiler off, although HM and CH were switched on and the house had gone cold. I switched the boiler power off and on again and the boiler lit up.

Does the above problem and its solution point to any particular component of the 3-way valve, or can anyone suggest how I might identify whether or not it is the motor, micro switch or valve that is acting up, assuming that it is the 3-way valve at fault.

 

[Hugh Jaleak]

If you are competent with a multimeter testing mains voltage then there is a good wiring diagram here: http://octaveblue.co.uk/c_heating/index.htm that may help identify what is or isn't working as it should.... If it proves to be the valve at fault, some allow the head to be changed without disturbing the water connections.

 

[MANDATE]

I don't know on what grounds you think the 3 port valve is faulty.
Regarding HW! there is nothing on the 3way valve that I know of that could prevent the boiler from working.
The programmer has a HW ON terminal which should be 'live' when HW is switched on,even though the the cylinder stat may be turn right down and boiler is not lit.
If there is no power coming from the programmer, then either the programmer is faulty or there is no power going into the programmer.
Likewise for the CH ON terminal, if that is also dead.
So first thing first, check out the wiring to the programmer.

 

[Slaydeuk]

Thanks for the link Hugh. The diagrams are very helpful. Mandate, it is my understanding that the boiler and pump get their power from the micro switches in the 3-way valve and these are actuated by the motor. So, if the motor doesn't operate or the appropriate micro switch doesn't work, the boiler stays off. This assuming that the programmer is working and either room stat or cylinder stat is calling for heat. It is unlikely that the thermostats are both faulty as they were both calling for heat at the time the boiler went cold. It could of course be a faulty programmer I suppose, but it would have to affect both CH and HW, as both were off, although both lights were on on the programmer. Whatever it is, switching power off and then on to the programmer cures it (temporarily).
The problem occurred last night and so far the system has continued to work happily. It would be better if it packed up completely.
I intend to wait for it to happen again and I will then carry out some tests to track down the problem. Trouble is that I tried this idea last time and the system then worked for 15 months without recurring.

Thanks for the input and I am still open to any further suggestions, or if my understanding of how the system works, as outlined, above is wrong.

 

[Agile]

It would be better if it packed up completely.

Most would say its better if it carries on working!

Something easily reset which only faults once in 15 months hardly seems anything to get very concerned about!

If you wanted more detailed advice in 15 months time then giving full details of your boiler and motor valve would be useful.

Tony

 

[MANDATE]

You're right in the sense that the boiler/pump gets its power from the valve via one of the micro switches. But this is only in the case of CH.
It is also true that for the above to occur the motor has to move the valve to CH position to trigger the micro switch.
Hot Water only is totally different. The valves motor is not energised, so it unwinds by return spring to HW position.
Power to operate the boiler/pump for HW goes from HW ON terminal on programmer to the cylinder stat, then across the stat and direct to boiler/pump. The 3way valve is not involved.
Even when both HW and CH are called for together, the room stat sends the valve to mid position but the power to operate boiler/pump still comes from the cylinder stat.
If you don't get HW or CH it could suggest both cylinder stat and room stat are faulty which is highly unlikely, so the problem is further back.
My logic suggests either a faulty programmer or more likely loose/ poor conection of the mains power going into the programmer giving intermittent conection.

 

[Slaydeuk]

You're right of course Agile, except that I don't know it's going to last 15 months. I like to go to warmer climes on holiday during winter months, which is just when the system will chose to pack up. Probably the best thing to do, as I obviously have a suspect system, is to replace the head of the valve (if the ball valve itself is moving smoothly) and, hopefully curing the problem. Trouble is I am a cheapskate and don't like replacing anything which doesn't need it. If it doesn't fail again before I go on holiday, I think I shall have to bite the bullet.

I've just watched a you tube video showing some tests you can carry out on the valve head which I might have a go at.

Further comments always welcome.

 

[Hugh Jaleak]

Make/model of valve?

 

[matt1e]

Its nothing to do with the valve

it's a problem with the boiler, cylinder stat, programmer or wiring

If the problem occurs when set on central heating only and hot water only then unless you have multiple faults you can also rule out the cylinder stat

Matt

 

[Slaydeuk]

Sorry about delay in responding, but got diverted. System working OK incidentally. Can't see a maker's name on the valve but it says Mid Position Automatic Code BGMVSP - 23 on the cover. British Gas I suppose.

The problem occurs with both CH and HW switched on by the controller and certainly the room stat calling for heat. I can't say whether the cylinder stat was calling for heat or not. If I understand the working of the valve correctly, if the cylinder stat was satisfied and the room stat calling for heat, the boiler and pump get their supply via a micro switch in the valve head. Thus requiring the correct movement of the actuator - or have I got it wrong. I don't have a wiring diagram of my system, but I am assuming it is set up as per the Sundial Y-Plan diagram I have downloaded as per Hugh Jaleak's suggestion earlier.

 

[matt1e]

The problem occurs with both CH and HW switched on by the controller and certainly the room stat calling for heat. I can't say whether the cylinder stat was calling for heat or not. If I understand the working of the valve correctly, if the cylinder stat was satisfied and the room stat calling for heat, the boiler and pump get their supply via a micro switch in the valve head. Thus requiring the correct movement of the actuator - or have I got it wrong.

No you are correct but the microswitch only comes into play whist central heating only is in demand

Now does the same problem occur when Hot water only is selected is so then it is not a problem with the valve (unless you have multiple faults)

Matt

 

[Slaydeuk]

Now does the same problem occur when Hot water only is selected is so then it is not a problem with the valve (unless you have multiple faults)

Matt

I'm afraid I can't answer the question as every time the problem has occurred CH has been switched on and probably also HW. It certainly was this last time, but the cylinder may also have been at temperature and the Cylinder stat open, thus leaving the CH only calling for heat.

I'm sorry to be so vague on this but it is a very intermittent fault which occurred several times about 15 months ago and only recurred once a few days ago. The worrying thing is that with cold weather coming up, if this happens while I'm away, I could have a freeze up. The Baxi condensing boiler is located in the garage where it is well protected by a froststat, but that's no good if the system is down. What you're saying is that it could be the boiler, the controller, the wiring the cylinder/room stats or the valve/valve head at fault. That doesn't narrow it down much. I would like it to fail so I could check a few things out, but it might not fail for another 15 months, if ever. I would welcome any tests I could carry out, to identify the fault, but if the fault is not present, I can't see how this is possible.

The last time this happened was in the evening when I noticed the house was getting cold. It was not really a convenient time to start tinkering with the system and I switched the power off and on and fixed it. I was hoping this might point to a likely faulty component.

 

[D_Hailsham]

This may help.

Mid-position valve operation and fault finding

 

[MANDATE]

You've not said what checks you've made so far or with what results.
Or do I take it no checks have been made?

Of course the problem is at the moment you haven't got a problem and
I agree its difficult to locate an intermittent fault.

If the fault occurs with CH only, then yes it could be faulty valve, wiring, room stat or programmer.
From what I gather, HW is also affected and the valve would not stop HW from operating. So the fault is common to HW and CH.
Both HW and CH are powered from a common source, which is the programmer.
To me either the programmer is maybe faulty or the power supply to the programmer.
Intermittent problems usually indicate loose connections, so why not remove programmer of its back plate and check the wire connections.
Of course the wires feeding power to the programmer will have connections further back so they also would need checking.
You will have a 10 terminal box, about 8 terminals being used to join wires together, so its worth checking those out as well considering it costs nothing.
Make sure terminal screws are tightened on the wire and not partially on the insulation.
Slight tug may reveal loose connection
You did say turning power off and on again at programmer switch seemed to cure it, so maybe the switch is the problem.

 

[MANDATE]

Duplicated!