More central heating peculiarities

[Dave Baker]

Further to the "no thermostat" thread a few days ago. So my oil boiler (Boulter Camray 2) has a Potterton controller/timer on the wall above it with two sliders for CH and HW that can be on, off, timed or "once". Below the controller on the wall is the master electrical switch which turns off the boiler and controller and the CH pump.

However as far as I can tell all the Potterton controller does is operate the two zone valves. The boiler itself never shuts off nor does the pump even when both sliders are set to "off". The boiler keeps on heating its internal water supply based on its temperature control knob and the CH pump keeps trying to pump it round which can't be very good for pump life methinks.

So is this just a case of unusual / incorrect wiring which could be easily corrected or is there a purpose to this arrangement I can't fathom?

I have managed to date (18 months) by using the electrical switch and the two sliders to turn things on every time I want heating or hot water and then putting them back off before bed or in the summer when I only want hot water just switching it on for an hour until the immersion tank is hot enough. It's not ideal and in the winter I wake up to a cold house but if I leave the CH on "timed" I can hear the damn pump resonating lightly through the rad next to the bed all night which keeps me awake. Also of course every time I switch off the master switch the controller loses its internal clock setting.

I would have thought that both the boiler and the CH pump (as well as the zone valves) should take their signals from the controller and if both switches are either "off" or in an off period of the timed operation then they should both close down and only fire up again if the controller calls for either CH or HW. Or am I just a hopeless romantic?

In the cupboard adjacent to the boiler, screwed to the wall, is a little square junction box (with no bloody cover on it!) the same size as a light switch box into which 6 cables run which are connected in some fashion by those transparent plastic terminal blocks which I associate with temporary wiring but what do I know.

4 circular three core cables run respectively to the boiler, pump and each of the zone valves. Two further flat grey cables disappear under the floor and I suspect then go back up behind the plasterboard to the Potterton controller and the master switch or maybe both just go to the Potterton. I guess each zone valve must need its own feed somehow but surely one cable must be a master to switch everything off in which case where is the third feed for the second zone valve?

I'm hoping that by some rearrangement of just the connections inside this junction box I can resolve the matter. No doubt I'm living in cloud cuckoo land.

I feckin hate electrickery and being profoundly colour blind doesn't help so I suspect I'll need outside help even if someone explains it all carefully to me. I'll be grateful for any advice though.

I have a pic of the junction box but it's not really possible to see how the wires connect without pulling them out of it so I'll not post it up unless someone thinks it might help them.

[Dave Baker]

PS. My system is a fairly close approximation to the S Plan layout here with two separate zone valves.

Except that there is no room stat anywhere and no cylinder stat as far as I can tell. Both the rads and the immersion tank just get as hot as the setting for the water temp knob on the boiler itself.

[Roger Mills]

I'm assuming from your description that you have an S-Plan system with two 2-port zone valves. See

This is *supposed* to work as follows:

The programmer and room stat drive the CH zone valve, opening it when heating is required. Likewise, the programmer and cylinder stat drive the HW zone valve.

Each zone valve incorporates a set of auxiliary contacts which close when the valve is open. These switch the boiler and pump on. When both valves are closed, the boiler and pump should *not* run.

Assuming that your system has been wired correctly, the symptoms you describe suggest that the auxiliary contacts in one of the zone valves have welded themselves together - so as as to switch the boiler and pump on even when the valve isn't open.

You need to find the cables which connect to your zone valves, and check them out. In your junction box you will find that the orange wires from both valves connect to one terminal, and both grey wires to another. Disconnect all of them - with the system powered down, of course - and check for continuity between each valve's orange and grey wires. They should both be open circuit with the valves closed. If there *is* continuity on one of them, the contacts are either welded together or the valve is stuck open.

From your description, it doesn't *sound* as if a valve is stuck open because this would result in the radiators being hot or the HW getting too hot when everything is supposed to be off. But it's easy enough to check. Each of the zone valves should have a lever to enable them to be opened manually. If all is well, you will feel some resistance when you operate each lever, and will hear the valve whirr closed when you let go of it. If the valve is stuck open, its lever will move freely back and forth as if it's not connected to anything.

HTH!

[Roger Mills]

Even so, if it's otherwise as per S-Plan, when both channels of the programmer are off, both valves should be shut and the boiler and pump shouldn't run!

[Dave Baker]

I've just run a lamp under there to try and see properly and I told you all a big fat lie. The two circular cables running to the zone valves are 4 wire not 3 although the two running to the boiler and pump are both 3 wire as are the two flat grey cables. So indeed, and as per your previous post, I'll have to work out the connection plan of the zone valve wires and then check for continuity in the appropriate places.

I'm now guessing the two flat grey cables both run to the Potterton controller with one for each zone valve and the master switch just turns the controller off which then turns everything else off.

So yes I'm now hoping it might just be a faulty zone valve. Well actually that would be an arse because they look like pigs to get at but still probably better than that the entire wiring system is not properly connected.

[Dave Baker]

Brilliant! I'm quite chuffed with myself. I've removed each zone valve in turn, fathomed its wiring and how the whole system works and checked that each zone valve operates properly when the CH or HW sliders are turned to "on" which they both do. I'm also pleased that both flow control knobs in the plumbing part of each valve move completely freely with no leaks. In the crappy system in my old house both of the sods had corroded up almost solid and also leaked and for the last few years I operated them with a spanner rather than chuck money at fixing something that was going to get scrapped in the end anyway.

So it looks like a micro switch as you say but my multi meter is awol so I'm stuffed for now but I'll try and borrow one. Then it seems my easiest method rather than disconnecting wiring inside the junction box is remove the zone valves again which is quick and easy and check that the grey and orange terminals are open circuit with the valves in the off position. If one is closed circuit then I've found my problem and presumably just need a repair kit for the motor part or a whole new motor depending on what's available. The two valves are different types so I guess one's already been replaced at some time.

I hope to god I don't have to change the type of valve if the faulty one is obsolete and have to start messing with the water part of the system too as each has a totally different plumbing installation.

[ARW]

+1

[Dave Baker]

Some more progress. Having established that the zone valves themselves work fine but currently having no multimeter I did the following.

Removing the orange wire from the HW zone valve auxilliary switch from the junction box but leaving the CH one connected the system is still on all the time.

Removing the orange wire from the CH zone valve auxilliary switch from the junction box but leaving the HW one connected the system works normally on the HW circuit. Off until the HW zone valve has opened fully and then the boiler and pump click into operation.

Conclusion. The auxiliary switch inside the CH zone valve is stuck in the on position.

Thanks very much for the help. I've learned a lot today.

The faulty zone valve is a Drayton ZA5. The auxilliary switch is soldered to the cable and it's a five minute job to swap the cable out if only it were available as a spare part. The synchron motor itself is clearly fine. Bit of a bugger to have to pay £45 for the whole unit just to get a 20p switch and the cable so I'll go on the scrounge. At a pinch I could even solder a new switch to the existing cable if I could find one of those in a catalogue somewhere. Any ideas?

[Dave Baker]

Sorted.

[Roger Mills]

Excellent! I thought it had to be something like that. What does the switch look like? I think most actuators use pretty standard micro-switches - obtainable from the likes of RadioSpares or Maplin - rather than anything fancy. Is it like any of these?

If you don't want to do any soldering, you may be able to crimp some mating connectors onto the cables which will simply push onto the spades.

If the switch is just stuck and not actually welded, it might be worth trying a bit of light percussive force on it. Does the switch's plastic plunger move in and out?

[Roger Mills]

Good. Sorry, should have read that before replying to your previous post!

[Dave Baker]

I checked it all out when I had it apart yesterday. The plunger moves ok and I also made sure that the cam on the motor operated it properly and wasn't holding it in all the time.

I'm mainly just pleased I now know what the problem is and I've learned a lot about how CH systems are wired and operate in the process so it's all good. I love learning new stuff even though I struggle on the wiring side of things with my colour blindness. With the other eccentricities in this house like the lack of any room stats I'd always assumed the way the boiler worked was a function of how it had been installed because it's been like that since I moved in. It wouldn't have occured to me it could be a simple component fault without your excellent advice.

Anyway it's perfectly liveable with until I get a roundtuit and everything else works fine so no worries. As long as the house stays warm and toasty this winter I'll not fret about any minor glitches.

[ARW]

For some reason Daves later posts were not showing when I added the +1!

[Roger Mills]

Anyway, he seems to be sorted - or at least knows the solution even if he hasn't implemented it yet.