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Wirsbo Controls

HowardHoward Member Posts: 57
Greetings fellow Wallies. As a service tech in the Chicago area, forced air outnumbers hydronics by a wide margin and radiant floors are still few and far between. I've just seen my first Wirsbo radiant system with Wirsbo controls. Much of it makes sense but there's a lot still unfamiliar. I'd appreciate help from anybody more familiar with these.

Each zone is controlled by a t87 thermostat with "Wirsbo" where "Honeywell" should be. There's no adjustable anticipator. 3 wires go to R,W and Y on the subbase. The customer had a 200+ page book showing dozens of wiring diagrams but I wasn't able to find one that matches exactly what I was looking at. One diagram showed the third wire going to transformer C and doing something with an anticipator. As I recall, I was getting voltage across R-Y regardless of call for heat so it's not set up as a call to close a WR 3-wire zone valve screw #6.

The thermostat connects to a printed circuit board(zone control module, ZCM) capable of serving 3 zones. Each zone has a yellow indicator light showing a call for heat and a red light showing a closed zone valve end switch. The ZCM has 2 screws on the left for R & C and 2 screws on the right, a pair of contacts to complete a separate control circuit to go turn on the circulator.

The zone valves mount to the top of the return manifold. The PEX tubing mounts below each zone valve. Tubing is about 7/8 od so id is 3/4 or 5/8. Yellow yellow is call to open. Red red is end switch. Some of the valves have beige plastic covers and the number A302XX0261. Others have metal covers with one slot and an indicator that is centered over a dot when it is tightened sufficiently. The metal ones have another slot with a pointer indicating open.

One of the 8 zones has too much heat and one has not enough. The problem zones are two small bedrooms with the beige valves. I suggested that the thermostats may be wired to each others' rooms. The customer says her engineer husband has spent a lot of time turning the thermostats up and down and would have probably noticed if that were the case.

More background: House built approx 1996. System is of similar vintage. Reset talks to motorized mixing valve. Customer moved in this past summer. Previous owner says some of the zone valves had been replaced. I don't know if the metal or plastic ones are original.

Okay, here's my question. Can these zone valves malfunction in such a way so that the indicator lights turn on and off in the correct sequence but the valve is stuck?I'd also appreciate any troubleshooting hints on these. You can't go into the room and grab a pipe then go to the manifold and feel the hot return.

Service Technician Extraordinaire (trying hard)


  • BrianBrian Member Posts: 285

    Try switching the zone valves without changing the wires.It sounds like they have the zones switched so that when one bedroom is calling,the other bedroom is getting the heat.
    Good Luck
  • Paul RohrsPaul Rohrs Member Posts: 357
    Valved manifolds

    The valved manifolds you described can also be fine tuned. From fully closed, it only requires 4ea 12 turns to reach the fully opened posistioned. Any more that that you will just be loosening the packing. One loop might need regulating even though the telestates open and close the valved portion. You would need to know individual loop lengths to accurately balance. Just a thought. Let me know if this is not suspected.

  • HowardHoward Member Posts: 57

    Thanks,guys--that was quick. So Paul, you're saying that by turning the head I can either eliminate leakage while shut or limit or restore the fully open position? Is clockwise less open? Brian, I'd be more inclined to swap the zone valve wires at the board if needed rather than swap the zone valves. Is it easy to remove the actuator without getting into water like a taco head? By the way, the manifold in question is in the foyer by the front door jammed in a partition of 2X4s. The Supply manifold appears to be an afterthought, completely obstructing access to the zone valves. Although the 1" copper and soldered coupling have some flexibility(yikes). The other pair of manifolds is in the boiler closet, a typical architectural masterpiece of maximum space utilization that makes me wonder if a scrap of PEX would leave visible bruises on an architect.
  • heatboyheatboy Member Posts: 1,468
    Are you sure of those........

    part numbers for the telestats? They are unfamiliar to me. They may not be Wirsbo heads? How many thermostats vs. telestats are there? With the ZCM, to operate more than one telestat with one thermostat, there needs to be a jumper from the #3 terminal where the therm is wired to all #3 terminals for the telestats you want controlled by that stat.That will power the additional heads open. I beleive there have been some issues with the T-86 thermostats in the past so you may want to look at that and possibly change it to a two wire Wirsbo (A3030101) thermostat. As you know, it's hard to diagnose from here ;-)

    Warm Regards,


    "Expert in Silent Warmth" ™

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  • HowardHoward Member Posts: 57

    Thanks, HB
    Each thermostat operates one telestat. I wish I had brought the digital. The photo is still in my 35mm instamatic. I guess i'm just fishing for the "I had one exactly like that--it goofed me up too--all you have to do is unsnap the fleegle schnokker and the pangriley will plop right in" sort of thing. Chances are Mr Customer will find that turning up the hot room makes the cold room hot and vice versa, then swap the corresponding 8 wires and I'll never see them again. But it's also likely that I'll be assigned to replace some of the zone valves(Where'd they get the name telestat?)so I'm just trying to learn my way around these components. Any idea what that 3rd thermostat wire is? I think it's electrically transformer C but it goes to the board so who knows. There could be some wacky algorithm for energizing the anticipator for some reason. The board didn't look much smarter than screws, a fuse, LEDs and relays though. Also, anything I need to know to replace a telestat? Like buy my wife 10 new bath towels and throw the old ones in the van? Grateful for any advice.
  • John AbbottJohn Abbott Member Posts: 348

    the thermostat you are describing sounds like a T86H Honeywell Wirsbo # A3010086.The third wire is for a parallel heat anticipator for radiant systems. I can't explain it's function but I have used them and have had no problem. The telestats if they are wirsbo have a knurled ring that simply unscrew.Two wires power the telestat and two make the end switch. You can trouble shoot with a voltage Tester and or tong tester to check for power to the telestat and current draw.The wiring for the thermostat and telestat usualy come with the zone control module. # A3030003 They may be available on line or if not and you need them I may have them in my truck and can scan them.The 200 page Book you refer to sounds like the CDAM I could never find the wiring diagrams in it myself

  • DaveDave Member Posts: 49
    Wirsbo controls

    We install many of these controls, as pointed out, perhaps the flow valve (under the telestat) is not properly setup for the length of the loop. The other problem that we have had is the HO "adjusting" the system. The knurled ring under the telestat must be set so that the indicator is pionted to the "dot" when it is not activated. We have found many of these that were moved from the initial settings. If nothing else a good radiant thermometer will tell you a lot about the system operation.
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