Control problem....?

[loughor]

Hello,
I was wondering if you could help me with my problem.
I have and S plan system - fully pumped HW and CH. Main problem is that the boiler and pump will not respond to the controller. Doesn't matter what buttons I press the system stays on. The only way to turn the system off is at the fused switch.

Components:-
Baxi Wm 532 boiler
Switchmaster 805 controller
Satchwell room thermostat - TLX 2356
HW tank thermostat
Sunvic SM5302 heating valve/actuator energise open/close - 2 port
Sunvic spring return hot water valve/actuator - 2 port.

Now, the British Gas engineer that came to look at the system, so as to check for having a service agreement, reckoned that I had a sticky valve. He took HW actuator off. Heating system was unaffected. Just had to manually turn valve for HW. (He also said boiler was too old to take on a service agreement!!)

So, following his advice (or as I interpreted it) I duly purchased not one, but two valve bodies which I have replaced and I have reconnected the existing actuators.

After reconnecting everything the system will not switch off. It seemed to me like the HW actuator was working fine previously but the CH actuator was naff (?). So I have repalced the CH actuator today thinking all would be well. No it is not. Still won't respond to controller.
The HW actuator does respond to the tank thermostat though.

The boiler and pump seem to be getting a live feed from somewhere and ignoring the controller. Could it be the HW actuator afterall????

I have cleaned room thermostat, checked all actuator wiring etc, all seems well.

I'm baffled as to what could have changed. Seems almost like I need to hit a "reset" button, but there isn't one.

Any ideas???

Pete

 

[brumylad]

are all the control components' wires linked together by a white plastic junction box about 6 " long or is it just a group of wires all coming out of the programmer.

Is there a frost stat built into the boiler or somewhere else in the system.

(I'd say the programmer is knackered)

 

[loughor]

There is a white plastic 5-pin male/female connector on the cable feed to each actuator.
One has 5 wires connected (CH = energise open/close) the other has 4 wires (HW = spring return).

I've checked the terminations in each connector and they are ok.

No frost stat fitted that I know of.

 

[ollski]

I would say that your microswitches are faulty on the hw actuator.....the easiest way is to unplug each actuator in turn and see which one stops the boiler

 

[croydoncorgi]

It's possible the motorised valves are wrongly wired. If the CH valve is motor-open, motor-close, this is the LESS common option on S Plan (which anyway is a Honeywell title, not Sunvic). If you wire a Sunvic MO-MC valve as if it was Honeywell spring-return, you WOULD get the symptoms you describe. Get hold of the Sunvic wiring diagram (this may be the one - http://www.sunvic.co.uk/minivaltypprog.pdf) and check your actual wiring against what the valve needs. Note that there needs to be wires from BOTH Call and Satisfied terminals on the roomstat to the CH valve.

 

[kevplumb]

bad link croydon

 

[felix]

I thought it might help if you had some idea how those actuators are supposed to work.

The one that's driven both ways responds to demands for CH (it opens) and No-CH (it closes) from your controller. Note that No-CH is a real wire with real volts on it, not just an absence of the CH demand.

The spring loaded one responds to demands for HW (it opens). When that disappears, the spring closes it. The tank stat breaks the HW command connection to the valve and the spring closes it.

When either valve reaches the fully open position an internal microswitch feeds live power to the boiler and pump. Like ollski, I think one of them is stuck or short circuit. Replacing the valve bodies was probably a waste of time.

Ollski's advice to unplug each one in turn is also good. A shut valve should not be powering the boiler. Remember that you'll have live terminals in that connector. Hopefully the male half will be on the valve.

PS: If you take them both off and the boiler still runs you've got a real puzzle to sort out. We'll burn that bridge when we come to it!

PPS: I should rephrase an earlier statement. I do not think ollski is stuck or short circuit ---

 

[kevplumb]

this

might help

 

[felix]

Well done that man. A picture certainly saves a thousand words. Loughor, just in case you don't spot it, where it says "live supply for other equipment" that means your boiler! It's also incomplete. That "L" on the room stat terminal 3 should be coming from CH demand on your controller and another wire from No-CH should go to terminal 2 (or white on the valve) to close it when CH is not required.

Actually, if yours really is wired this way a faulty valve actuator can't be the problem. The boiler supply would still depend on both the controller and the room stat. But maybe, as croydoncorgi suggests, it's wired wrong. You'll have to have a look.

PS: I've just re-read the original post carefully. Did you have this problem BEFORE you sent for Gasman or did you get him in for a something else?

 

[loughor]

Thanks for all the replies, certainly a few things to look at there! Starting with unplugging the acctuators I think!

Felix - problem was there before the gas engineer inspected, (it's one of the reassons he was called) hence his indication of the "sticky" valve.

My MO-MC valve is wired exactly as per kevplumb's link - including the orange wire- as shown in the upper diagram.

One other point. I'm sure the MO-MC actuator was in the "open" position before I connected it to the valve/electrical supply. It is now closed. Something closed it but kept the live to pump and obiler. Could it be a faulty room thermostat?
Pete

 

[felix]

A correctly wired valve would close when connected if either the controller or the room stat said No-CH. If you're struggling with that diagram I don't blame you because it's very misleading.

There are effectively TWO motors in there, though they may be on the same shaft. One is on yellow for Open and the other is on white for Close. They have a common neutral connection. Each is in series with a spring loaded switch that opens when the valve reaches the end stop. The switch feeding the Open motor is a changeover type. When the valve reaches the fully open position, that switch takes power off the motor and out through the orange wire instead.

When you plugged your open valve in, something (controller or room stat) was saying "I don't want CH" by putting volts onto the white wire. The valve's Close motor ran until the valve hit the end stop and opened the switch. If power was ever reaching the boiler through orange, this disappeared before the valve even moved - always assuming that the wiring is correct!

Try unplugging the HW valve instead.

 

[loughor]

Well. just got home.
1. Switched off the power then unplugged the CH actuator.
2. Switched power back on and the pump/boiler started up as before.

3. Switched power off again, reconnected CH and disconnected HW actuator.
4. When power was switched back on nothing happened! No pump, no boiler and no response from anything, when hitting buttons on the controller.

HW actuator is a Sunvic SZ 2301, by the way.

From what I've been reading this probably means that the HW actuator, or the limit switch in it, is is to blame?????? Do all limit switches click when operated? (I've taken it apart and this one doesn't)

If it is the limit switch and seeing as I have a spare actuator from the CH loop, could I use a limit switch out of that actuator? Or just buy another HW actuator?

Pete

 

[felix]

Switches that work generally do click. Everything is now pointing to yours being faulty and so it doesn't click. You will need an ohm-meter to make a definitive test. You will also need a meter to make sure that the switch you take from the spare actuator works the way you want it to. If you're determined enough you can rig up a continuity tester with a battery and torch bulb.

I'm somewhat surprised that you couldn't get the boiler and pump to do anything at all with the HW valve unplugged. The CH should still have worked.

 

[loughor]

I've ordered a new HW actuator today, rather than mess about with limit switches. I'll pick it up tomorrow and see if it solves the problem! I'll report back with the news, hopefully good news.

Can I thank you all for taking the time and effort to help me with this problem. Your replies have been of great assistance to me.

Fingers crossed!

Peter

 

[namsag]

As Olski said days ago sticking microswitch common fault on all types of motorised valves don`t know why people start suggesting wiring faults etc on an existing system that have been in twenty odd years. takes two minutes to remove wiring to check which valve head is faulty