No gas: the regulator. Episode forty-five of the Gas Service Animated series.

The regulator's whole job is to take a higher, varying supply pressure and hand the house a steady, low one. A spring pushes a diaphragm open; the downstream pressure it's feeding pushes back. When the house draws gas, pressure dips, the spring opens the valve; when the draw stops, pressure rises and the valve closes — that's lock-up. It's a balance, breathing through a vent to the outside air.

And it's the number-one reason you'll find a live meter but no gas in the house. The meter's fine, the inlet's there — but nothing, or almost nothing, comes out the other side of the regulator. When that's the picture, this is your suspect.

The most common failure is debris. Dirt, rust, pipe scale, a smear of pipe dope, a chip of thread sealant, even weld slag — anything that rides downstream and lands on the regulator's seat or orifice. A scratch a tenth of a millimeter across is enough to let pressure creep at no flow; a real chunk holds the valve so it won't pass gas at all. A dirty gas stream is a regulator's enemy.

Now the hidden one — the vent. The regulator has to breathe: that little vent lets the diaphragm feel outside air so it can reference atmosphere and modulate. Plug it and the regulator goes deaf. Mud-dauber wasps build in it, spiders web it, paint seals it, snow and ice cap it. A blocked vent is one of the top causes of low or erratic gas that nobody thinks to check — so on a regulator call, look at the vent screen first.

Regulators freeze off, and there's real physics behind it. When gas expands across the regulator, it cools — roughly six to eight degrees for every hundred pounds of pressure drop. Add the moisture that's always in the gas, and on a cold, high-demand morning ice forms right on the diaphragm and the regulator quits modulating. One frozen regulator can take down a whole building or block, not just one house.

The diaphragm itself can fail — hardened, cracked, or ruptured. Then you don't get steady control: you get hunting and oscillating pressure, or excessive venting, or the outlet collapses. It's the moving part that's flexed millions of times, and eventually it gives.

So you diagnose it the same way every time. Inlet pressure present, outlet low or gone. Then narrow it: tap and inspect the vent — is it clear? Is there ice on a cold day? Is the regulator dented or damaged? Is it even the right size for the load? The code puts a union at the regulator so it can be swapped — but on the utility side of the meter, that swap is utility work.

A cold-morning call. Meter inlet's strong, but the house is starving — weak flames, dropping pilots — and it started overnight when it hit the teens. You pull the vent screen and it's iced shut. That's a frozen, blind regulator. You've found it; clearing and preventing the ice is the utility's regulator to handle.

The regulator in one breath. It hands the house a steady low pressure, breathing through a vent. Debris on the seat, a blocked or iced vent, a Joule-Thomson freeze, or a failed diaphragm all read as inlet-yes, outlet-no. Check the vent first, and it's the utility's to swap. Next: the safety devices that shut you off.