Boiler doesn't turn on but zone valve opens
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.