Centaurstat 7

[JT]

I have a Horstmann Centaurstat 7 programmable room stat. It gives the appearance of working OK. It clicks at the right times etc but the heating circuit in the zone that it controls doesn't close down when it teaches the set temperature, despite the appropriate click.

Normally I have the programmer set to constant for this zone. If I change this to off or timed it switches everything off correctly. Even if I remove the Centaurstat body from the backplate the circuit continues to work (if on at the programmer)

I tried a re-set (set and enter buttons) to no avail. Would a replacement unit solve the problem or is it something else?

Any suggestions most welcome. Many thanks.

[cj]

Hi JT Basically any room stat is just an on/off switch regardless of how clever it appears to be. Whilst not familiar with your model most stats when removed from their backplates disconnect from the system.( when you take it off ,no wires are still connected) If this is the case then the programmer is wired wrongly.

From your post it seems the system works fine if on 'Timed' but if set to constant the stat does not work. Again suggesting a programmer fault or wiring fault at the programmer.

To verify run the system on constant ,remove the stat (turn off power first it may be mains switching) make sure no wires are connected to the stat ,insulate any bare wires ,return power . If system still works the fault is either in the programmer or a secondary junction box.

We really need more information for further help. What type of boiler do you have ? What type of system (fully pumped 'y plan' etc) What programmer controls the system?

to start.

HTH

CJ

[JT]

Hi cj

Thanks very much indeed for your help

"> Basically any room stat is just an on/off switch regardless of how clever it

This is exactly the case

The system has been running fine for 6yrs so, with respect, I doubt if this is the case

Whether on timed "on" or constant at the programmer the circuit is "on" and is not turned off when the thermostat is apparently satisfied. When turned to off or timed "off" at the programmer the circuit is off.

Tried this and with only the base plate remaining, the circuit remains on (dependent of course on the settings at the programmer)

Glow Worm. Ultimate 80 FF

Fully pumped two zones plus water to tank all with 2 port valves.

Horstmann H37 3 channel

(not sure that it's series 2)

[JT]

">> Many thanks again. The system has worked absolutely fine for

That is with no stat in place, just the baseplate with exposed terminals. No voltage when turned to off at the programmer

Tested for continuity between the prongs of the stat when removed. (Lower fits to common on the base plate, middle to call and upper to neutral)

Continuity between lower and upper when set to low temp; lower and centre when set to high temp.

[JT]

Correction Apologies see below

Correction *Upper not connected to neutral. The neutral lead is connected to a blank on the base plate*

[cj]

Hi JT sounds like the stat is controlling a zone valve somewhere hence the switching on high & low settings it could be that this valve is stuck open so even when the stat (satisfied for heat) calls it to close it remains open ,could also explain readings at stat backplate. Of course sods law will probably point to the new mirror you just fitted being nailed through the stat wires shorting them out.

In any event the stat does not appear the problem unless the backplate is broken causing a short,you need to investigate the wiring further I'm afraid.

A tip for motorised valves feel around the front end for a thin protruding piece of steel this is a manual opening device. Move it and if no resistance is felt the valve is open if it feels hard to move and you hear the valve whirr as you move it the valve was shut and you are forcing it open.

Maybe other on group may have other ideas but for now

HTH

CJ

[JT]

Hi again

You really are very helpful and I'm really grateful. It's a real puzzle and I'm determined to solve it.

I guess if the valve is stuck open then that zone will heat up even when switched off at the programmer, if the water or zone 2 circuit is on! Will check that tomorrow. Also will ask whether the good lady wife has been hanging decorations! I feel sure as you say that the stat is OK. Glad I didn't buy a new one.

[ARWadsworth]

A wiring diagram is here for you

I would guess at the S plan plus.

The valve may only be partially open/stuck and so not making the microswitch contacts it usually makes when fully open. You idea or trying the other zones off is a good one.

Adam

[JT]

Many thanks

The valve seemed to be working fine, controlled by the progammer as suggested by CJ

So disconnected brown wire between valve and stat feed at junction box. Still both common and feed terminals at stat backplate live when progammer on. Tried disconnecting common to stat at the junction box. Both common and feed now dead! Seems like there is short between the common and feed between stat and junction box. This fits as it was the only piece of cable not replaced when the whole system was refurbished 6 yrs ago. Propose to fit rf stat, mounting receiver next to junction box and use my Centaurstat on Zone

2, which at present has non-programmable stat. Does this sound reasonable?

Thanks again both.

[ARWadsworth]

Does this sound reasonable?

Try this first. Rewire your prog stat with some flex to the existing system (close to the wiring centre and just for testing purposes) and disconnect the stats old wiring whilst you do this. If things work ok then it is the prog stats wiring that is at fault.

Adam

[JT]

[JT]

Sorted! Removed Centaurstat and attached it temporarily at the junction box to the terminals where the suspect wires entered. Everything working fine. Dodgy cable.

Many thanks for help cj and Adam.

[cj]

YVW glad you sorted it .

CJ