How to Reconnect a Radiator

Steps:
1. Start by shutting off the boiler and the cold water feed to the boiler.
2. Drain the system using a hose and vent each radiator in the house.
3. Remove the temporary caps using the pipe wrenches. When using the wrench, be sure that it touches the pipe in three places so it does not damage the pipe.
4. Disconnect the spud from the radiator valve.
5. Apply the pipe dope to the threads of the spud and seal it with the single strand wicking.
6. Using the spud wrench, carefully tighten the spud in position. Be sure the threads correctly catch to prevent damage to the spud.
7. Apply the pipe dope and wicking to the pipe coming up through the floor.
8. Thread the other half of the radiator valve onto the pipe, again being cautious of cross threading.
9. Tighten the radiator valve using the pipe wrenches. Once the valve is in the direction of the radiator, it can be reconnected.
10. Wrap the ratchet straps around the legs of the radiator and put a 2×4 or another piece of scrap wood into the strap. Using the 2×4 as a lever, carefully pull the radiator into position with the valve. It might help to wedge shims on the other side of the radiator to hold it in place. You can use multiple levers if you need to adjust the height as well.
11. Once the radiator has been moved so it’s perfectly aligned with the valve, connect the valve to the spud using the nut that connects the two.
12. Once the connection has been made, tighten it with a wrench.
13. With all the work done, turn the cold water feed and the boiler back on and vent all the radiators again.

Lesson from the Field: In one This Old House project, a homeowner attempted to swap out a leaking radiator valve on his own, but when he went to loosen the valve from the radiator, the supply line sprung away from the radiator, creating a gap he couldn’t bridge. The problem? Muscling the pipe over without using leverage can cause it to bend, throwing the connection out of plumb. That’s why using ratchet straps and shims — rather than brute force — to draw the radiator into alignment with the valve is so critical.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, explains the importance of the union connection: the valve and the spud are two separate parts, and a nut brings those two pieces together — that’s why it’s called a union. Understanding this connection is key, because if the spud and valve aren’t properly aligned before you tighten the union nut, you risk cross-threading and a leaky joint.

Resources:
All the tools Richard used to reconnect the radiator, including wrenches, pipe dope, wicking, and the radiator valve, can all be found at home centers and plumbing supply houses.

Pro Tip: Richard prefers using pipe dope combined with single-strand wicking for thread seals on radiator connections rather than Teflon tape alone. As he describes it, this is a “tried and true method” — especially important when connecting new work to old piping, where a reliable, leak-free seal is critical.

About Bushings: Radiators typically have large-threaded openings — often two inches — and bushings are used to step down to the size needed for the valve. A bushing has threads on the outside and smaller threads on the inside, acting as a reducer. They come in many size combinations, so if the existing threads are damaged, you can go up to the next largest pipe size and use an appropriately sized bushing to bridge the gap. Be sure to always drain the heating system before beginning any radiator valve work.