When a hydronic boiler quits in cold weather, the house has two problems at once. The first is comfort. The second is the water sitting in the pipes, which can turn into a repair bill faster than the boiler ever will. ACHR News has a piece titled Repair or Rent? Making the Right Call When a Boiler Fails, and its summary states that "getting it back online is the priority." It also notes that when repairs take days or weeks, temporary heating can keep a building operational. That framing is useful, but a homeowner should put the pipes first, then build the temporary heat plan, then wait on the repair decision.
Confirm What Is Actually Down
Start with the boiler's own indicators. Photograph or write down the display code, the status light, and the pressure gauge reading before you touch anything. Many boilers lock out after repeated failed ignition attempts or when water pressure drops below the fill range. A lockout is not the same as a dead appliance, and the code tells you which one you have. Compare the cold fill pressure on the gauge against the label on the boiler, and follow the manual's fill procedure if it is low. If the pressure keeps falling, look for a leak before you top it off again, because a system that keeps losing water is hiding a problem.
Check the circulator next. If you have a clamp meter, clamp one conductor of the pump supply while the system is calling for heat. A reading of zero amps means the pump has no power, has failed, or is not being called. A steady reading with a cold house points the search back toward the boiler, the zone valves, or the thermostat wiring.
Protect the Water Side First
Pipes freeze where the heat is weakest. Look at exterior walls, crawlspaces, garages, rim joists, and any run that passes through a cold attic. Open the cabinet doors under sinks on exterior walls so warm room air can reach the supply lines. If the house is heading toward freezing, let the most exposed faucet drip slowly so the water keeps moving.
Draining the system is a service decision, not a reflex. Shutting the main and draining a hydronic loop only makes sense if you have a plan to refill, bleed the air, and restore pressure afterward. A drained loop refilled with air pockets can leave you with a noisy, underperforming system and no heat. If your loop uses glycol, check the concentration before any drain or top-off, because glycol is part of the freeze protection and changing its strength changes the margin.
Temporary Heat Without a Bad Circuit
Portable electric heaters are the common stopgap, and the load math is where most people get into trouble. A 15-amp, 120-volt circuit is generally limited to 12 amps for continuous loads, which works out to about 1,440 watts. A single 1,500-watt heater can overload that circuit by itself. Add a second heater, a hair dryer, or a space heater running on the same circuit as a kitchen appliance, and the breaker becomes the least of your problems. Use the clamp meter to see what the circuit already carries, then run one heater per circuit. Skip extension cords and power strips for heaters, and keep clearance around every unit.
Fuel-burning portable heaters, gas ranges used for heat, and generators do not belong indoors. Carbon monoxide is the hazard here, and an alarm is a last warning, not a plan. Test the CO alarms before the cold night arrives, and replace any that are expired or not responding.
Log the Outage So the Repair Decision Has Numbers
Keep a simple log with the time the boiler went down, the error code, the outdoor temperature, and the indoor temperature at one fixed spot twice a day. Record which heat source is running and what each one costs to operate. This log matters for the repair versus rent question. If the technician says parts will take days or weeks, you can price keeping the house livable for that stretch instead of guessing. The ACHR News summary ties the same question to temporary heating for keeping buildings operational, and your house is the building. The log turns a vague worry into a line item you can compare against a repair quote.
Have the Details Ready Before the Tech Arrives
Gather the boiler's model and serial numbers, the nameplate voltage, the error code, the gauge reading, the circulator current reading, and your outage log. Ask whether the repair visit includes a parts check, since a technician who knows what is on the truck can often shorten the wait. Keep the crawlspace hatch open if the supply lines run there, and keep the thermostat where it was so the system can respond the moment it returns. A boiler outage is easier to manage when the pipes are protected and the numbers are written down.