On 9/11/2011 12:21 PM, Tom Horne wrote:
On Sep 10, 5:23 pm, wrote:
On 9/10/2011 1:58 PM, Selk Perkner wrote:

I have an older Weil Mclain gas steam boiler for the radiators in my
house. If the electricity goes out, it won't run -- I believe it needs
electricity to operate the gas valve, and the thermostat is also wired
into a circuit.

Should electricity go out to the house during the winter, I could
certainly get by for a few days with flashlights and coolers as long as
there is heat. I have instructions for running the boiler manually, and
could connect a battery operated thermostat, but would prefer to run it
on a backup electrical connection if possible so I don't have to babysit
it in the dark.

Good idea, most gas utilities won't even allow a manual bypass gas valve
for obvious reasons since it bypasses all safety devices.


"manual bypass gas valve .snip. since it bypasses all safety devices."

That is simply untrue.

Okay, it bypasses essential safety controls.

The manual bypass does bypass the
thermostatically controlled solenoid gas valve but it does not bypass
the pilot safety shut off system

not really much help if someone opens the bypass and lets the burners
operate. The pilot already did its job at that point.

over temperature cutoff, or the

the gas valve is now turned on manually. No over temp cutoff is in play.

pressure limit safety. And nothing bypasses the pressure relief
valve!

There is no pressure limit safety when the gas valve is manually bypassed.

The typical failure mode is that the water gets boiled off and the
boiler turns red and sets the house on fire. BIL has his doctorate in
engineering and owns an engineering firm. They do an extensive amount of
accident investigation work and that info (and pictures) came straight
from him.

He already said that he had the instructions for running the
boiler manually. When such instructions are provided the safeties are
all mechanical because electrically actuated safeties fail safe and
prevent operation when the electricity is absent.

Then why do you think the gas utilities in our area (one is a national
outfit) will not allow a manual bypass to be installed?


There is a single electical conduit running into the boiler which is
connected to a box with an on-off switch above the boiler, as well as a
line running from the thermostat.

The thermostat is obviously a straightforward job, but is it a
straightforward job to switch the power at the on-off switch from the
regular house current to a backup source? How much capacity will this
backup need -- does it pretty much need to be a gas generator, or can I
get by with a battery backup of some sort?

If it is just an old natural draft boiler without inducers or other
electrical loads a UPS would work. If you wanted an elegant solution
there are UPSs that can be hard wired. In that case you wouldn't have to
do anything to switch over since the UPS would do it for you.


Is this just a quick project in the event of a major winter outage
(assuming I buy the parts ahead of time) or should I get the guy who
does the annual inspection do the work? I've done plenty of basic
wiring like running cable for new outlets and lights and switches, so
I'm not intimidated by basic stuff, but also know better than to mess
with stuff beyond my pay grade.