Michael Gallagher wrote:

Hello,

I'm looking into getting a Weil-McLain Ultra Boiler installed this
Spring. I've done research on it, and came across a quote that
bothers me a little: Someone saw it at a home repair trade show and
said that it never shuts down, it modulates up and down. Now, does
that mean it never shuts down AT ALL, even when the temp gets to what
the thermostat is set at; or that it never shuts off while the heating
system is running, and goes off when the thermostat doesn't need
anymore heat? I've assumed the latter is true, but it wouldn't hurt
if someone who knows this system confirms that. Thanks.

Mike

It will shut off when the demand is low enough. There is a minimum safe
flame level on any burner system below which the gas valve must shut
down. During periods of high demand, e.g. cold outside, it may very well
run continuously. The Ultra regulates air/fuel mixture to maintain high
efficiency burn. It's actually higher in efficiency at low fire, which
is one good reason to have a modulating valve.

hvacrmedic