Radiator Leaking? Valve, Vent or the Radiator Itself

Water at the valve stem

What it looks like. Water around the spindle, just under the knob or the thermostat head. Stelrad says a valve leak often starts when the spindle packing becomes worn or damaged.

A thermostatic valve. Oventrop’s first fault for a leaking valve is a loose gland nut: tighten it. If its O-ring is damaged, Oventrop fits a new gland nut without draining, because the valve has an extra seal, but not on its AV6, ADV6 and RFV6 series. Danfoss says the gland seal on its RA 2000 valves can be replaced in a few minutes with the system running, but on steam it says to consider doing it during an off cycle. On any other valve, follow Burnham’s rule: cool and no pressure first.

A steam valve. HUD’s Rehab Guide says the stem packing on most radiator inlet valves wears with time, and the valve can be repacked. Hoffman says an ordinary two-pipe steam supply valve has a packing nut that tightens that packing.

Fully open or fully shut. On one-pipe steam, Castrads, Hoffman and Peerless say the valve is never left halfway; Peerless says that holds water back in the radiator and causes hammer. DOE says a valve that will not fully open or shut may need replacing.

Water at the joint between the valve and the radiator

What it looks like. Water at the big union nut where the valve meets the radiator, or at the threads where the pipe goes in.

Try a small turn. Viessmann’s advice for a dripping pipe fitting is to try tightening the connector a quarter turn with a spanner, since a seal may have come loose. Do it with the heat off and the radiator cool, and stop if it does not move easily.

When the seal has gone. Viessmann says corrosion can wear seals away, and then a qualified heating contractor replaces them. Myson says the straight threads on its column radiators need professional sealing. On steam, DOE says leaks at threaded connections or the inlet valve seal may let steam into the room.

Shutting one radiator off. On hot water, Castrads says the water leaves through a second valve at the other end, the lockshield, and Stelrad says to turn off both valves before working on a leak. Castrads says a thermostatic valve still lets a little water through unless the decorator’s cap made for it is fitted.

Water from the bleed screw or air vent (hot water)

A bleed screw. It should only let water out while you bleed. Danfoss says to turn the heat down first, and both Danfoss and Viessmann say to close the screw as soon as water comes out. If it still drips once closed, have a heating technician look at it.

An automatic vent. On the Bell and Gossett No. 97 and the Caleffi 5026, the makers say the cap is opened one turn to vent and screwed down tight to shut the vent off. Both say a vent that leaks or is corroded must be replaced, and Caleffi says that is work for qualified personnel, with the pressure at zero and the water below 100 degrees.

Two makers’ own rules. Resideo says the red cap on its EA122 must be tightened all the way, by hand only, never with tools. Taco says never to take the cap off its Hy-Vent.

Vent it cold. Bell and Gossett says only to vent by hand below 100 degrees and to keep out of line with a vent’s opening. Weil-McLain warns that water from an air vent may be very hot.

Bleeding all the time. Castrads says frequent bleeding may mean a problem with the system. Have a heating technician find it.

A steam vent that spits water or hisses steam

What is normal. Hoffman says vapor or slight moisture from its 1A and 1B radiator vents is normal, but steam passing through all the time means the vent has failed. It says to replace them as needed or every 10 years.

A vent that blows steam. Xylem says a vent that keeps discharging steam may have a collapsed float or a pinhole leak, and cannot be repaired: replace it. Fit the new one with the heat off and the radiator cold; Heat-Timer says its opening faces up.

A vent that spits water. Heat-Timer says vents clog over the years with rust from the radiator and pipes. Its fix is to take the vent off with the heat off, as Danfoss says, soak it in hot vinegar for 30 minutes, wrap the thread with Teflon tape and refit it. Do not overtighten it, and watch from the side when the heat comes back on. If it still blows steam, replace it.

Danfoss’s list. For a spitting vent, Danfoss’s one-pipe steam valve instructions say to check the radiator’s pitch, open the supply valve fully, check the riser air vent, and check for too much pressure. HUD says the radiator should slope slightly toward the valve, with a shim under the feet farthest from it.

Too much pressure. Hoffman rates its 1A vent for a maximum of 1½ psig in use, and Weil-McLain says typical one and two pipe systems need less than 2 psig. Bell and Gossett says a setting above the vents’ rating can hold them shut. Ask a technician to check it.

Wet steam. DOE says wet steam can make the master vents on the steam pipes leak water, and that a common cause is oily residue in the boiler water after pipe work. Weil-McLain says a boiler whose water line jumps about because of dirt or oil is skimmed by a technician. Hammer is in a boiler making noise.

Water from the radiator itself

What it looks like. A wet patch or a rust stain on the radiator, between two sections, or a pinhole that weeps. Stelrad says rust inside eats away at the metal until it makes holes.

Cast iron. Castrads says pinholes or damaged joints in very old cast iron radiators are usually repairable, at a cost. Burnham’s instructions for joining sections warn that a missing gasket or a forced thread makes the radiator leak.

Steel. Stelrad says a radiator that leaks from corrosion has to be replaced. Myson’s warranty does not cover rust from oxygen corrosion. If it is a fairly new Runtal radiator, Runtal says to tell it at once if a defect is suspected, and the US guarantee on Purmo radiators holds only if they were not repaired or changed without approval.

Stop-leak. Weil-McLain says never to use petroleum-based sealing or stop-leak compounds, because they can damage system parts. Stelrad says leak sealer is only a short-term fix.

On steam, take it out of use. NYC’s housing agency says a steam radiator with corroded pipes or faulty valves can rupture without warning and release high-pressure steam. Close its supply valve fully and check it holds, and if you rent, tell the owner at once.