Malfunctioning thermostat

[sos]

We have 3 zones of in-floor radiant heat. Two zones work fine, the third is 'on the blink' (see below). We have "Dual Sensing Digital Thermostat" units from Watts.

The thermometer icon in the display is only described as indicating that the numbers show current temperature. The thermometer icon on the non-working thermostat is blinking. What does this mean?

I have shorted the thermostat control line at the thermostat (goes to the Taco box in the boiler room) and the pump and heat come on like they are supposed to. This tells me the problem lies with the thermostat. No matter what the temperature setting, the flame icon does not show up and the pump doesn't run via thermostat.

It uses a floor sensor (no air sensor) and worked fine up to this week. I have tried putting in freshly recharged batteries (in place of the original alkaline) to no avail. The reported floor temperature is reasonable, it just doesn't activate the heat when well below setpoint.

Thanks,
Steve

[Christopher]

Steve,

The blinking thermometer means that it's hit a temperature limit somewhere. Since you're only running off of floor temperature, this can only be the floor limit.
Go into your configuration and see what the FH (Floor High) limit is set to. The system will not heat the floor beyond this setting, no matter how you program it.

[sos]

Thanks much Christopher, your answer makes sense even if it doesn't match what my thermostat is doing (see below). When I called in to the office and asked what the blinking thermometer meant, they said "we have no idea". They said it was bad and another is being delivered to me (no idea when).

My configuration does indeed have a Floor High limit. It was set at 74.5F. The thermostat set point is 70.0, actual temperature varies with time of day, around 68 now. I tried raising FH to 77 anyway, we'll see what happens.

Also note that setting J6 (selection of sensor) is set to "Air", see next.

The insides of my thermostat aren't what I expected. There is only a place to connect a single sensor (i.e. two screws not four). I have a hard time understanding how this thermostat is dual sensing with only one set of connections. Yet the programmable settings are clearly for a dual setup (J6 has the option of AF and Flr).

Steve
who is still confused

[Christopher]

Steve,

If your J6 setting is set to air, then what is displaying on the screen is the air temperature. The air sensor is built into the actual DualTemp itself, which is why you can't see it.

So what is going on is that the system is regulating your air temperature (the displayed temperature), and the floor limit was set to 74.5. The blinking thermometer means that it was trying to raise your air temperature to 70 (which is where you have it set), but since the floor was already at or over 74.5 (the FH setting), it couldn't fire.

If you only want it to regulate and sense the floor temperature, you need to set J6 to Flr. It will then display the floor temperature, and work to heat the floor to the set point. In this mode it will not care about the air temperature at all.

[sos]

Excellent, you have put all the pieces together in a way that makes sense.

Does Watts have an application guide for setting the PID parameters? Given the air/floor sensor setting being wrong, I'd like to make sure the rest of it is set up right. We are in an earth sheltered house--all concrete, so the thermal time constants are pretty long.

Steve