can I replace and old wirsbo 2 wire thermostat?

elgatowis

I bought a home with all radiant heat, it has like 25 zones, one in each room, and hallway. It has old school wirsbo 90's thermostats with a dial. I tried to replace these with a newer wirsbo digital thermostat but since my old ones are not powered it does not work. I tried a simple cheap thermostat no luck. I am not sure how these old thermostats work, if I take the two wires out of the old thermostat and connect them together to close the loop it does not open the valve, the ony way the opens is if I use this wirsbo thermostat and turn up the temp. Is there some kind of special resistance this thermostat is providing the system? very strange.

Steamfitter66

I believe its a tekmar rtu

please post a pic of the stat and the control panel.

Mark Eatherton

Pictures...

Of not only the thermostat, but also the control valve operating device, which I assume is on the distribution manifold. (telestat)



If there is mercury on the inside of the round Honeywell looking thermostat, it is just a switch. You could be dealing with a bunch of dead operators.



If the operator is the old heat motor style of operator, Wirsbo had a special thermostat developed for use with that operator that would send small pulses of electricity to the heat motor, so that when it did finally call that it didn't have to wait 7 minutes for the valve to open and respond. I (inadvertently) found that if THAT particular thermostat is connected to a motorized type of operator, these quick bursts of energy will cause the zone valves to open and close like 12 times per hour (once every 5 to 7 minutes) for just a few seconds. It was marketed as a "radiant" thermostat. Only problem was, the wholesalers who were selling it (and the installing contractors like moi) didn't read the instructions to find out how many cycles per hour it produced. I almost lost a customer over them because we were using them on Honeywell motorized zone valves, and he complained of short cycling. But when I showed up, the first thing I'd do is turn the thermostat WAY up, and got no short cycling. It was when the stat was at or near set point that this condition showed itself. We ended up going back and replacing like 200 of these incorrect thermostats. To their credit, Wirsbo paid us (traded tubing for labor) to replace them, and it really wasn't their fault. It was the wholesalers fault for misrepresenting the product and its application…



A picture of your mechanical room wall (especially any blue boxes) would also help.



ME