Replacing A Radiator Valve

by Josh on September 27, 2006 · 31 comments

in Uncategorized

There isn’t much that can go wrong with a hot water radiant heating system. According to reliable Shrewsbury plumbers I know, it is basically a second plumbing network that just circulates water between the boiler where water is heated, and radiators that release that heat into the rooms. When trouble occurs, one common problem is failure of a radiator valve. Fortunately this problem is easily corrected.

The valve for the radiator in my office has been leaking slightly since we bought the house, allowing water to seep out around the stem leaving ugly rust and scale running where water trickles down the supply pipes. There’s no telling when this tiny leak could suddenly worsen and make a real mess, so I want to deal with it right away. Replacing a radiator valve is a simple plumbing job that took me less than half an hour with the system already drained.

Please note: I am not a plumber and I do not know all the proper terminology for the parts and process described below. These steps worked for me, but follow these instructions at your own risk.

Tools for the Job:

  • Two pipe wrenches
  • Spud wrench
  • Heat gun to loosen paint and expand plumbing joints
  • Teflon tape
  • Plumber’s teflon putty, aka “pipe dope”
  • Coarse steel wool and small metal brush to clean old pipe threads
  • Utility knife to score paint covering plumbing joints
  • New radiator valve (duh)
  • Safety gear: glasses, gloves, respirator if you suspect lead paint

Here’s the broken valve disconnected from the radiator. Note the rust and water scale on the valve and supply pipe. When disconnecting this union joint, remember that the nut is removed toward the radiator, not toward the valve (I’ve made that mistake before). Removal also goes more smoothly if you use the heat gun to expand the outside member of the joint to be unscrewed and then use the utility knife to score any paint that was lapped over the joint.

Old valve disconnected

Next remove the old valve from the supply pipe and insert the spud wrench. Whenever possible, use two pipe wrenches when unscrewing a fitting. Here I used one wrench on the valve to remove it, while I used a second wrench to hold the supply pipe stable. This lessens the chance the pipe will be bent or sheared when the valve is removed. The fitting that connects the valve body to the radiator is called a spud. It is removed using a spud wrench, which looks like a prop for some alien technology from a sci-fi “B” movie. The grooves down the sides of the spud wrench grip a pair of nubs on the interior of the spud when the wrench is inserted.

Spud wrench

Use one of your pipe wrenches with the spud wrench to remove the spud. Be sure to use the heat gun to warm up the radiator so the spud will come out more easily. Even after doing this, removing the spud still took enough torque to radially deform my spud wrench a bit. (Lousy alien technology…)

Removing the spud

With the old valve completely removed, now is the time to clean up any corrosion or paint around the joint and threads. Use a wire brush, steel wool and the utility knife to clean things up a bit. Take care to protect yourself and anyone else in the house from paint chips that may contain lead. Minimize dust spraying the surface with water during any fricton-based paint removal, and vacuum up paint chips and dust with a HEPA-filtered vacuum right away. Disconnect the new spud and nut from the new valve and wrap the spud threads with teflon plumber’s tape. Put a little pipe dope on top of the tape and install the new spud and nut using the spud wrench and pipe wrench. Make sure the nut is on the spud the right way before installing the spud.

New spud installed

Tape and dope the supply pipe threads and then install the new valve body following the two-wrench method used to remove the old valve. Tape and dope the threads of the union fitting between the valve and the spud and then tighten down the union nut. Wipe off any excess pipe dope and celebrate your accomplishment by reinacting your favorite sci-fi movie scene using the spud wrench as your prop: “Khaaaaaaaaan!”

New valve installed

The true test of any plumbing repair is whether it holds water. I’ll have to defer that step just a bit until I have a solution for the radiator I removed from the upstairs bedroom. I may not be completely ready for heating season, but at least I’m making progress.

{ 30 comments… read them below or add one }

Patricia W. September 28, 2006 at 5:04 am

Excellent how-to! One of my supply knobs are broken off in my house and I’m scared to death to do my own fix. I always wondered how those bizarro long wrenches worked too.


nadja and sean September 28, 2006 at 10:33 am

Great job! When we first started working with radiators, it all seemed very intimidating!


Josh September 28, 2006 at 11:54 am

Plumbing intimidation isn’t completely bad. Some friends of ours have a broken radiator valve which a previous owner “repaired” by replacing the worn-out internal valve parts with a carriage bolt and caulk. They wish that PO had been intimidated enough to get help from someone who knew what to do.


marvin March 17, 2008 at 8:41 am

Just curious. Did you have to remove the spud with its union, or could you have reused it and just attached the valve to the existing union not?


doug September 1, 2011 at 12:57 pm

I strongly recomend replacing the spud with the new valve. I tried to use the old spud and had alot of leakage, then re drained and got my handy, dandy spud wrench and put the new spud in. Everything was fine then.


Josh March 17, 2008 at 3:57 pm

Thanks for the question, Marvin. I suppose it might have been possible to connect the new valve to the old spud and union on the radiator, but I didn’t try this myself. I used the new parts because I knew they fit the thread size for the valve and because it allowed me to get rid of the painted (read: lead hazard) old union.


John November 11, 2008 at 1:00 pm

So where do you get this type of Spud Wrench? When searching online, “spud wrenches” look like pipe wrenches.


Josh November 11, 2008 at 1:20 pm

I got my spud wrench at my local hardware store. Call around or stop by a hardware store (not a warehouse-style home center) located in a neighborhood of older homes. If they don’t have a spud wrench in stock, the store clerks will probably know where to get one nearby.


John November 13, 2008 at 3:03 pm

UPDATE: FYI- Apparently there are no more independently owned hardware stores in the Chicago area. They all seem to be part of the Ace chain which does not carry this tool. There is a 150 year old hardware store in Joliet and a Berland’s House of Tools… neither one knew what this was. Local plumbing supply houses are charging between $30 & $50 until I found one that only charged me $20 and it was special order. The tool suppliers don’t carry this either. This is common $15 tool when Googling “Radiator Spud Wrench” however it depends on what part of the country you live in when looking for it locally.


Josh November 13, 2008 at 4:57 pm

What a saga, John! The shop where I got my spud wrench (in stock– no special order) is an Ace Hardware affiliate, but I know from visiting a few different Ace locations in my neighborhood that the stock from store to store can vary greatly. I know I didn’t pay $50 or even $30 for my tool. $15-$20 sounds about right.

Isn’t it funny that it was more work finding the tool than it will be using it?

Closed circuit to Chicago hardware stores: you’re missing a sales opportunity in a city full of old houses with radiators.

P.S. Two years after the repair described in my original post above, the new valve is still working perfectly and the radiator remains drip-free.


Ralph Rodway November 17, 2008 at 5:14 pm

i want to replace a vent valve on a radiator in my house. Unfortunately, the threads on both the old valve, and the radiator itself are stripped. any ideas on how to proceed will be greatly appreciated..



John November 17, 2008 at 7:07 pm

“i want to replace a vent valve on a radiator in my house. Unfortunately, the threads on both the old valve, and the radiator itself are stripped. any ideas on how to proceed will be greatly appreciated..”

I would drill it out to the next NPT size up and re-tap new pipe threads. Then simply install a reducer bushing and a new vent valve.

You probably have 1/8″ NPT now. Since pipe sizes are measured from INSIDE the pipe, your hole is not going to be 1/8″. The next NPT size is 1/4″.

Small pipe thread taps & handles are inexpensive. Just be sure and get the exact size drill bit for that tap size. Also make sure the tap is NPT. Threaded pipe is tapered… regular taps cannot be substituted for NPT taps.

Use plenty of tapping lubricant and go slowly, backing out often to clear the chips. If you’ve never used a tap in metal, consult a friend with some metal working or machinist experience… taps are brittle and if you’re not careful can break off in the hole.

And finally, since the threaded hole will be tapered, you can only tap it down to a specified depth.

here’s a chart:


David March 3, 2009 at 2:08 pm

Can anyone recommend a particular brand of valve? I’ve seen a few different manufacturers out there. Most appear to be built / priced comparable. With most of them made in China.

Any recommendation would be great.



Josh March 3, 2009 at 3:10 pm

David, it sounds like you have done more research on this than I did. I just went to the local hardware store that I trust and bought what they stocked. It is a “Mueller/B&K” valve made in China. It felt solid and has worked without a problem for the 2.5 years since I installed it.


Derek Stanley June 16, 2010 at 9:44 am

Is it posible to repace a Radiator valve on the lower floor without draining down the heating system? delboy wishes to know?


Josh June 16, 2010 at 11:23 pm

So far as I know, Derek, you’ve got to drain the system. Gravity will make trouble for you if you disconnect a radiator with water in the pipes above it.


Aub July 16, 2010 at 3:43 pm

Well done, and simple how-to. I have a question regarding the function of the valves. Are the valves supposed to control the heat variably? That is, if I just open the valve a wee bit, is it supposed to just give me some heat, and if I crank it fully CC-wise, is it supposed to be lava? Presently, there isn’t a valve in my house that does anything at all but let water in, and I think it would be nice to be able to control the flow, or even shut off certain rooms. Feedback is greatly appreciated!


Josh August 7, 2010 at 8:05 am

Sorry for the delayed reply, Aub. Yes, radiator valves can be used to manage the heat an individual radiator produces. By restricting the flow of new hot water into the radiator you will produce a radiator that is cooler than the others on the system. It’s an inexact process, but closing radiator valves can be useful to zone heat or balance the heat distribution

Here’s what I mean: I my house the thermostat is in the center of the main floor on the dining room wall, so the whole heating system turns on or off based on the temperature of that room. If I wanted to save energy by not heating the upper floor bedrooms during the day, I could close their radiator valves in the morning, shut the door to the upstairs, and then open the door and radiator valves again in the evening when I wanted the bedrooms to warm up a bit. But I can’t reverse this at night and close down the main floor radiators because the thermostat is on the main floor (and my pipes could freeze in our delightful Minnesota winters).

If your house is heating unevenly here are some other ideas. If you have an individual room (on the perimeter) that is always too warm, you can dial back the radiator flow to make it cooler. If the rooms on the perimeter of the house don’t get warm enough–and not just next to a drafty window– you could dial back the radiator in the room with the thermostat, so that more heat is added to the system before it cycles off.

You also can by thermostatic radiator valves, Aub, though they are subject to the same system-level considerations I mentioned above. Thermostatic valves would be most useful in the upper-level zoned cooling scenario I mentioned, or to reduce temperature in a room that is chronically too warm. Unlike the heating system thermostat, however, thermostatic radiator valves can’t signal the boiler to add heat when a room cools too much.


Matt October 3, 2010 at 10:54 pm

Great article definitely will help me out in the future I’m sure. I am having trouble with my vent valves and would like to replace them. Most are siezed up and just keep breaking keys to open them.I tried soaking them in PB Blaster and WD-40 but no luck. Currently I have been unscrewing them to vent the radiator but I am afraid of stripping them out or cross-threading them over time. Does anyone know where I can find new vent valves? I have no problem finding new keys but the valves seem to be impossible to find.


Josh October 4, 2010 at 6:48 am

Matt– I assume you’ve tried asking around at neighborhood hardware stores, but most of the stores around me (True Value, Ace, etc.) stock radiator air vents. Alternatively, I found a couple options for you at Amazon: Cobra air vent with key or Ace Air Vent


Scott Mandrell October 16, 2010 at 12:29 pm

Any ideas about getting the union out if the ‘nubs’ are broken off? I have a spud wrench and have used it several times with success. However, I (for some reason, I don not know why) broke the ‘nubs’ on one radiator. Aach! So, I was considering sawing off the coupling collar and trying to remove the pipe with a standard pipe wrench. Any thoughts? Hurry, I am getting anxious about doing something soon.


Josh October 16, 2010 at 5:26 pm

That sounds like a reasonable plan to me, Scott. You might also want to ask yourself why the inside of the union broke. Is it heavily corroded at the radiator? Were you turning it the wrong way? Heating up the radiator with a heat gun, and using some penetrating oil at the joint between the radiator and the union should help loosen things when you are ready for the pipe wrench.


Abdul Hakeem October 18, 2010 at 5:51 pm

Thanks for the great advice it really worked. Keep up the good work


Robert October 26, 2010 at 6:35 am


Well four years out of one blog equals impressive. Of course I found your blog after completing the job of removing and replacing the valve and the spud. I still need a spud wrench (this is what was originally sort after when I found out the name of the tool needed) because I’ll be dealing with 17 radiators and will need this tool. Removing the spud without the tool is not too difficult. You can use a saw. A good ol’ sawzall is perfect. First, cut back from the collar close to the pipe but leave about 1/4 to 1/2 for ‘grip’ and cut right thru this section. Next on the inside diameter of the pipe cut down into it but not all the way! Do this in two or three sections about 3/4 of an inch away from each other. You can then use a cold chisel to bang in between the cuts. This will help break the brass off the inner threads. Be careful not to ‘egg’ (deform) the spud as you chisel. If needed make a few more cuts on the other portion of the spud and then chisel them. At this point you should be able to turn the remaining spud out with a wrench. It will give very easily even after being there 50 years. Just remember to be ever so careful not to cut the inner threads……… Many have said that using the spud wrench here just breaks off the nubs…. but tightening in the new spud is more difficult without it.


Josh October 27, 2010 at 5:11 pm

Robert, thanks for detailing such a helpful technique for freeing a stuck spud. I could visualize the steps and really learned something with this one.


Roger November 12, 2010 at 8:43 am

Thanks!! For as much plumbing as I have done, you’d think I would be familiar with this type of repair..Your plan was excellent. Thanks for sharing!


Michael X January 25, 2011 at 12:51 pm

I wish that I’d seen this earlier before I started my endeavor to replace the same angle valve. In the end, I did install the valve, but the union nut is overworked and would not firmly connect the spud to the valve without leaking water condensate once the steam was up. So I had to leave the valve shut. I used pipe dope and teflon tape but it didn’t help. Now I need a spud wrench seems like, to replace the old spud with the new one that comes with the valve. Luckily the local store said they have spud wrench for $14. Can’t wait to pick it up tonight!

Thanks for sharing the experience in such a detail.


Dominick February 8, 2012 at 2:34 pm

Hi, I have the same problem with two of my radiators on the second floor. I’ve tried bleeding them but both radiators remain cold. The control valves no longer function. They will turn continuously. My question: Is there a particular technique for draining the radiators on the second floor? (i.e. Do they have to be drained? Do the radiators on the FIRST floor need to be shut off? (they give heat but the valves do not work). Thank you


Robert September 30, 2012 at 7:29 pm

I wish i had a spud to remove. The readiators in my house are piped up with bushings and unions. When i tried to replace a bad rad valve in my dining room which is where the thermostat is. I quickly discovered i was in trouble. First i tried running in the bushing towards the radiator in order to provide room to turn out the valve. This failed so i tried running the bushing out towards the valve and it dislodged from the radiator but is still wedged between the two. I can probably get it out with a hammer and then begin the joyful task of removing the valve. My question is this. Can i install the spud into the radiator and once the valve is fixed or replaced install the unions, one on the radiator and one on the valve. I will only have about 2 1/4 ” spacing between the two? I’m assuming that this is te proper installation and not the bushings and union combination? Any help you can offer will help-Thanks.


Nicholas Geti January 26, 2013 at 6:13 pm

Relating my experience with radiators. I have a 200 yr old house with a hot water radiator in every room. They needed some cleanup to go along with redecorating the rooms. There were three different brands of cast iron radiators and several kinds of valves although all the valves had the same dimensions and were interchangeable. Forty years of leaking valves caused a heavy buildup of lime and green corrosion.

I discovered that modern valves and fittings even by the same mfg of mine have a different flare angle and face dimension. So, I decided to repair them instead.

I was able to disassemble all the valves and remove all the crud by soaking/brushing in hdrochloric acid. Then I polished them with a wire brush in a drill. They came out looking brand new.

I repacked the stems with Valve Stem Packing (corded Teflon 1/8″ diameter) made by W.L. Gore & Associates


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