View Full Version : Boiler doesn't turn on but zone valve opens

10-23-2010, 01:31 PM

I have a radiant floor heat system with a boiler and three zone valves. There are 24V simple honeywell thermostats. The thermostats are wired into the correct pipe zone and valve. Each of the thermostats opens each corresponding valve, however only one thermostat actually turns on the boiler (gas ignites) and pump. The other two only opens the valve, and does nothing to the boiler.

Each of the zone valves appear to be wired correctly. Each of the red wires are wired to the other two corresponding red wires in the other valves, and the to the + and - of the 24V transformer. One of the yellow wires in each valve are all wired together, and the other yellow wire in each is wired to the thermostat.

Is it just a case of bad valve ie, re and re valve?

thanks for any advice.

10-23-2010, 02:30 PM
Do you have a controller for the zone valves? If so, it may have what is called an 'end switch' that closes when any one of the zone valves is calling for heat. This gets wired to the boiler to request heat. Also, depending on the boiler controls, it might not fire if it is already within the min/max setting of the aquastat, so that could be normal.

Did this ever work 'right', or is it a new install/configuration? There are lots of ways to setup and configure a boiler, so it is hard to be exact without more info on exactly what you have.

10-23-2010, 03:19 PM
This did work "right" at some point, that is, each thermostat would turn on the boiler/pump. I had to replace the pump and transformer last winter, and it hasn't worked the same way since, so wanted to sort it out. There isn't a controller for the zone valves as far as I can tell.

There are the four wire zone valves (two red and two yellow). One set of red are wired together and to a +'ve on 24V transformer. The other set of red are wired together to the -'ve on the 24V transformer. One set of Yellow is wired together and to the -'ve on the 24V transformer, and the other set of yellow are wired individually to each of the thermostats, the return from each thermostat is wired together and to the +'ve on the 24V transformer.

I'm not sure how the transformer is wired into the boiler, but power for the boiler comes from the box behind the transformer. The transformer has 5 or 6 terminals on it.

All three thermostats are wired together and into the boiler/transformer the same way, which is why I thought it was a bad zone valve. I wasn't sure how a zone valve could open from the thermostat, but not activate the boiler.

I understand about the min/max of the aquastat, however, even when the boiler is completely cold, the two thermostats will not turn it on. The 3rd thermostat does.

I should further explain that if I set the two "non-working" thermostats on (which results in no heat), and then turn the third thermostat on, all three zones get heat until the third zone thermostat is turned off, or reaches it's designated temperature.

10-23-2010, 04:30 PM
Look at the one that works right and compare it with the others. Unless your boiler has additional inputs to enable multiple thermostats to turn it on. you need another part to 'OR' the requests for heat together and connect it where the one that works triggers things. I'm not all that familiar with the zone valves. It is possible that one set of leads is actually just a switch, and you could tie all of them together to trip the boiler to turn on. See if you can find the spec sheet for the zone valve and post it. It may become obvious after you've looked carefully at the one that works and compare it with the spec sheet.

Okay, I looked at the 5000 series spec sheet. The yellow leads are what connect through your thermostat to open/close the valve. The red leads are just a SPST normally open switch. So, those leads are what you need to 'OR' together to turn on your boiler (which I assume will turn on the circulator). So, one red from each of the zone valves would go to the common of the 24vac, and the other three would go to the boiler's thermostat input. Then, any one of those switches that closes because of the thermostat, would apply the 24vac to the boiler to turn it on. Compare what the one that works does.

10-23-2010, 09:35 PM
thanks for the info. I will try it in the morning.

10-24-2010, 07:40 AM
Can you post a schematic? Do you have a multimeter?