Pipe plug in tapping on a cast iron radiator (C) Daniel FriedmanRadiator Plug Removal & Repair Procedure
How to remove a cast radiator plug to install an air vent

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Radiator repairs: how to get out the cast iron plug.

When a steam heating system was later converted to forced hot water heat someone would have removed the steam vent and plugged its mounting opening.

At that time the installer should have also installed an air bleed control valve near the radiator top. But some installers may have omitted the vent at one or more radiators. The result is a radiator that never gets warm or never gets warm enough.

Here we describe how to get out a stubborn, painted-over or rusted-in-place plug in a cast iron radiator. Speaking from experience we also describe what goes wrong and how to get out of that new level of trouble.

Page top photo: a painted-over square-sided pipe plug in a cast iron radiator. This is probably plugging a steam vent connection in a radiator converted to hydronic (hot water) heat.

Green links show where you are. © Copyright 2017, All Rights Reserved.

How to Remove & Replace a Painted-in Rusted-in Pipe Plug or Air Bleeder From a Radiator

Pipe plug in location where an air bleeder valve is needed at a cast iron radiator (C) GGIf you have already removed an old pipe plug or air bleeder vent from your radiator or if you don't anticipate any trouble getting the old one out, the procedure at AIR BLEED VALVE INSTALLATION will suffice.

If you are faced with removing a painted over and rusted-in-place pipe plug or broken radiator vent some removal and repair suggestions are given here.

Question: how to replace a radiator pipe plug with an air bleeder valve

I would like to know how to remove the small cast square plug on my cast iron radiator and install a manual air bleeder valve.(See attached photos)

Once the plug removed - will I need to thread the hole for the bleeder ?

I came across this interesting article on a website - Removing Worn Bleed Screws - [given below - Ed.]

Based on that article - my square plug would be a bleed screw ?

Do you know where I can purchase a Bleed valve replacement kit with tap wrench on a canadian or USA website ?

If it is to hard to remove the bleed nut or screw - wouldn't it be easier to make a new hole on the opposite side and install the new bleeder ?

- Anonymous by private email 2017/12/14 [Click to enlarge any image]

Reply: try to remove the plug without breaking it off, then install an air bleeder valve

Iron pipe plug at  reader GGI nervous about this answer because we both know what can go wrong.

Your radiator sports what looks like a conventional pipe plug in the bleeder opening, not a radiator bleeder valve.

Regarding that square-headed plug / bleeder, I'd also not expect such a device to be made of other than brass as raw steel will corrode enough that the valve seat will have a short life.

The silver colored bleeder valves you see in some radiators or for sale are typically chrome plated brass or steel [shown below] .

Make this test: scrape away the paint from the square end of your plug and see if it is brass or iron.

Air bleed valve components for hot water heat (C) Daniel Friedman

OR you might just confirm that the plug is iron using a magnet.

We often find that cast iron radiators that were originally connected to a two-pipe steam heating system will have a plug in this location (near the top of the radiator).

That's because the steam vent on a radiator was often located lower on the radiator body.

Steps in Removing An Old Radiator Plug

Tapping in cast iron radiator used for a steam vent (C) Daniel FriedmanOur photo shows a typical tapping in a different cast iron steam radiator, after a steam vent or pipe plug has been removed. This American-Radiator Company antique radiator, located at 190 Bowery in New York City, was not in use. This offers evidence that it is possible to remove old rusted fittings from a tapped opening.

Liquid Wrench penetrating lubricant at

Keep Calm and Carry On.

Air bleeder valve ready for installation (C) DanieL Friedman

How to Repair a Broken-Off or Stripped-Thread Radiator Air Bleeder Opening & Valve

Typical radiator air bleeder valve in a Brooklin NY home (C) Daniel FriedmanRadiator air vents or air bleeders normally have at least two components: a tapered valve, typically brass, whose point seats into a mating, machined brass seat. Unscrewing the valve permits air to vent from the radiator.

The whole air bleeder assembly apparatus then being screwed into the vented radiator.

If the radiator's tapping intended to receive the air bent is badly damaged it can often be repaired by drilling, tapping, and inserting a wire thread insert.

Above: a typical chrome plated air bleed valve in a cast iron radiator - this one is in a home in Clinton Hill in Brooklyn NY. You'll notice that the mounting body of this vent is hexagonal rather than sporting the characteristic square shape of a cast iron or steel pipe plug.

Watch out: having broken off parts and hurt myself a time or two I've learned not to assume that everything will go according to plan when working on plumbing and heating systems. It's helpful to be prepared for trouble.

If the threads of the air bleeder tapping in the radiator are absolutely destroyed or if you break off the plug and have to drill it out, then you'll need to tap an oversized hole and either tap to the diameter and threads of a larger radiator vent or you'll use the tap-repair kit we mentioned previously and that I'll describe in more detail here.

A helical screw repair kit involves over-drilling the hole, tapping new threads into the hole (that's not as hard as it may seem), screwing in a threaded sleeve whose outer diameter matches the drilled, tapped hole, and whose inner diameter and threads match the vent to be screwed into the sleeve.

Recoil wire thread inserts and tools for repairing damaged tapped or threaded openings - at and cited in this articleillustration: an example of a wire thread insert used to repair a drilled and tapped opening in a cast iron radiator (or other iron or metal parts). There are various forms of threaded inserts and similar terms may be used to find them including wire thread inserts, helicoil thread repair kits and thread repair kits.

These parts are from Recoil - cited just below.

These helicoil repair kits used to be widely used in the automotive industry when we changed spark plugs so often that we over-tightened and stripped the spark plug hole in the engine.

["We" here means me and my '65 Mustang whose spark plugs lasted about 9000 Km between changes. ]

Obviously the inner threads of the sleeve have to match those of the plug or radiator vent to be inserted.

The outer threads match the diameter of the tread tapping tool that matches the drill size that's used to drill out the opening.

Thread Repair Kits & Penetration Oil for Repairing for Cast Iron Radiators

A typical thread repair kit will include the following:

  1. Drill bits in appropriate sizes
  2. Taps to cut threads into the drilled-out opening
  3. Possibly a thread cutting oil to assist the tapping.
  4. Inserts that thread into the tapped, drilled opening
  5. Tools to insert the insert

The choice of drill size and tap size and then insert size is made to suit the original threaded opening and original fitting. An over-size hole is drilled and an insert installed to reduce the new opening to the original or required threaded opening size and thread pitch to match the device (such as a radiator air bleed valve) that is to be installed.

The "sleeve" or insert in many thread repair kits is essentially a helical spring that is inserted and sealed into the receiving body. has no business nor financial connection with any manufacturer or service provider discussed at our website. We do not sell products nor services.

What About Just Removing the Pipe Plug, Bleeding Air, Replacing the Plug?

It is also possible to bleed air from a radiator manually by simply removing a conventional pipe plug if that's what's screwed into the opening.

Watch out: The hazard of this approach is that as heat rises in the system you'll get dirty hot water spewing out of the open hole and you'll be frantically trying to start and then screw in the plug.


Continue reading at AIR BLEED VALVE INSTALLATION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see EXPANSION TANK AIR VALVE LEAKS for leaks at the air adjustment valve on a boler expansion/compression tank


Or see these

Radiator Air Bleeder & Vent Articles

Suggested citation for this web page

RADIATOR PLUG REMOVAL at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

Or see


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman