Plumbers were busy Thursday, very busy.

Doug MacMillan answered 30 calls. Gary Stone had 15. And they’re just two out of 21⁄2 pages of plumber listings in the phone book.

“I’m getting calls for frozen pipes,” said MacMillan, of MacMillan Plumbing Inc. “But nothing burst, just yet.”

Pipes may not reveal their ruptures until the weather warms up enough to melt the ice inside. Warmer temperatures are on order today and into the weekend, still below freezing but closer to the January average, according to the National Weather Service.

The new year started in Bend with overnight temperatures in the single digits and there they stayed. Thursday morning dipped to 1 degree, according to NOWData — NOAA Online Weather Data. The low Monday morning measured 9 degrees.

“It seems to be a basic recipe for disaster — single digits,” said Gary Stone of Gary Stone’s Plumbing Service, Redmond. “When it’s not above freezing for two or three days, when we get into where the phone won’t stop ringing.”

The worst offenders are those folks who left their garden hoses attached to an outside faucet. The ability of frost-proof exterior pipes to stay that way is their ability to drain. They can’t drain if the garden hose is left attached.

“They should have removed exterior garden hoses from faucets weeks ago,” Stone said.

The weeklong cold snap is the chilliest in a number of years, according to NOAA. The coldest day of January 2012 dropped to 10 degrees. The coldest day since 1981 measured -5 degrees. Normal temperatures this time of year are in the low 20s, according to NOAA data for Bend.

“In order to keep pipes from freezing, you have to create a non-freezing environment for pipes to live in,” Stone explained.

That means insulating pipes where they need to be insulated. In some cases, homes plumbed during the recent housing boom in Bend were left exposed in the area beneath the insulated floors, he said. The only way to determine if those pipes are properly insulated is to crawl into that space beneath the home.

“That’s where the spiders live,” Stone said. “And it’s dark and dirty.”

If a pipe within an exterior wall freezes, do not apply heat to it and leave it unattended, Stone said. It may spring a leak once the ice inside melts. The frozen pipe, if it’s not designed to expand, may already have burst. Only the ice is keeping it from becoming a geyser.

PEX pipe and fixtures expand and contract without cracking if the water inside freezes; some plastic pipe will shatter, copper sometimes will split, said Scott Jolly, office manager at Sweeney Plumbing in Sisters. He said he received a handful of calls for service on freezing pipes Thursday, as well.

To prevent frozen pipes, all three plumbers advised keeping the home warm and outside air vents closed. “Keep the place warm and buttoned up as tight as you can,” said MacMillan.

Where plumbing runs through exterior walls, keep a faucet open to a drip to keep water inside moving, said Jolly. Open cabinets beneath sinks to allow warm air to circulate around plumbing, they said.

Know the location of your main water shutoff valve in the event of a leak. Also, if a pipe bursts or leaks, shut off power to your electric water heater or the gas supply if it’s gas-fired. Once the water drains from an electric water heater, the element inside is exposed and may break, just like a light-bulb filament, only more expensive to replace. And remember to disconnect the recirculation pump for the hot-water system, if you have one.

In the event of a leak or burst pipe, all three offered the same advice: Call a plumber.