Tankless hydronic boiler provides hot water but not heat

Tankless hydronic boiler provides hot water but not heat

by Will
(Charlottetown, PE, Canada)

I have a three zone tankless boiler set up at my recently purchased home. I have hot water but not heat. When a thermostat calls for heat the circulation pump turns on but not the boiler blower. When a thermostat is turned up so it calls for heat (this goes for all thermostats), it's respective zone head will open it's valve.

The relay in the aquastat is seen to be engaged but the boiler doesn't fire up, although the circulation pump turns on.

I replaced one of the zone heads with a new one and it worked (the boiler would turn on with the circulation pump) but only for a few days. With the initial success after changing the zone head with a new one, I thought maybe all the zone head end switches had blown for some unknown reason. I then replaced an end switch in a second zone but it the situation remained unchanged for that zone head (the boiler did not fire when the T-stat called for heat).

What would be the cause/source of the problem? What/Where should I check? Thanks for you help.

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