Step-by-step guide for fixing a leaking radiator valve. Clear tools list, simple steps, pressure targets, and testing tips contractors can use on any job.
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On most jobs, a small drip can turn into a big mess fast. Fixing a leaking radiator valve is simple when you follow a clear plan. In this guide, we explain what causes the leak, the tools you need, and how to stop it for good. We cover packing gland fixes, union weeps, and full valve swaps. You’ll see pressure targets, PTFE tips, and timeframes. If you’ve got water on the floor and a client on your phone, this shows you how to act fast. It’s straight talk and real steps you can do today.
To stop a leaking radiator valve, isolate the valve, drain 2 buckets (about 10–20 liters) if needed, then tighten or repack the gland, or reseal the union with 10–15 PTFE wraps. Refill to 1.0–1.5 bar, bleed, and recheck after 30 minutes. If corrosion is heavy, replace the valve.
Small leaks have a few common sources. Knowing which one saves you time.
Spot the source first. Dry the area with a rag. Use tissue to track the drip. Work from top to bottom.
Have the right kit ready before you shut water off.
Get the system safe and the work area ready.
Most contractors skip photos. Don’t make that mistake. Take quick photos of settings before you start.
Follow these steps in order. The goal is to stop the leak and leave the system balanced.
Identify the leak point Dry everything. Wrap tissue around the gland, union, and compression. Watch where it wets first.
Try a gentle gland tighten On the spindle gland nut, tighten 1/8–1/4 turn. Don’t overdo it. Open the valve and check. If it still weeps, proceed.
Repack the gland Close both sides. Crack the gland nut and lift it slightly. Wind PTFE string once or twice around the spindle (not too thick). Reseat the nut and tighten gently. Reopen the valve and test.
Reseal the union to the radiator If the union leaks, close both sides. Place a bucket. Loosen the big union nut (commonly 24–30 mm). Drain 2–5 liters. Remove the nut and check the radiator tail. If it uses a fiber washer, replace it. If it’s a tapered tail, add 10–15 wraps of PTFE tape on clean threads. Refit and tighten snug, not brutal.
Reseat a compression joint If the pipe compression joint weeps, back off the nut. Inspect the olive. If it’s scored or oval, replace it. Add a smear of jointing compound if you use it, or 3–4 wraps of PTFE on the olive. Reassemble and tighten firmly while supporting the valve body.
Align and support Misalignment causes repeat leaks. Ensure the valve, tail, and pipe sit square. Support the opposite side with a second spanner to avoid twisting the radiator.
Partial valve replacement (if needed) If the body is damaged or seized, plan a full swap. Drain the radiator fully (5–10 liters for a typical panel). Replace like-for-like: 15 mm, 1/2" BSP tail. Use 10–15 PTFE wraps on the new tail. Fit a fresh olive on the pipe. Tighten both ends while supporting the valve.
Reopen and pre-check Close the bleed screw. Open the lockshield and valve 1 turn each to pre-fill the radiator. Check for drips for 2–3 minutes.
Bleed air Open the bleed screw a quarter turn with a key. Catch air and water. When water runs steady, close it.
Restore settings Return the lockshield to its original position (e.g., 1–2 turns). Set the TRV or manual valve as requested.
Testing is where many call-backs start. Slow down and verify.
If you’re also looking to streamline professional proposals for small callouts like this, our guide on professional proposals pairs well with these steps.
Not every leak needs a new valve. Use these simple rules on site.
Repair it if:
Replace it if:
Typical replacement takes 45–90 minutes including drain, swap, refill, and bleed. Quote clearly for parts, inhibitor, and testing time. If you need help with pricing structures, check our advice on invoice templates and clear scope notes.
Usually no. For fixing a leaking radiator valve at the gland or union, you can drain just that radiator. Close the valve and lockshield, loosen the union, and catch 2–5 liters. Drain the whole system only for widespread valve swaps or major corrosion.
For most 1/2" BSP tails, 10–15 wraps of PTFE tape works well. Keep wraps neat, tight, and in the thread direction. On the gland, PTFE string used sparingly seals better than thick tape. Too much material makes assembly hard and can crack parts.
On sealed systems, refill to 1.0–1.5 bar when cold. Many contractors aim for about 1.2 bar. After bleeding air, top back up to the same level. On vented systems, just restore the header tank level and ensure the feed and expansion pipe are wet.
Turn the boiler off. Working with hot, pressurized water is risky and makes leaks worse. Let it cool 1–2 hours. Close the radiator valves, control the drain, and repair safely. You’ll do a better job and avoid burns.
Most gland or union fixes take 30–60 minutes, plus 10–15 minutes of testing and bleeding. Full valve swaps run 45–90 minutes depending on access, paint, and alignment. Add time if you’re replacing multiple valves or dosing inhibitor.
Fixing a leaking radiator valve is about three things: identify the leak point, seal it correctly, and test under heat. Use 10–15 PTFE wraps on tails, refill to 1.0–1.5 bar, and recheck after a full heat cycle. Next steps you can take today:
When you wrap up emergency leak jobs, tools like Donizo help you turn quick voice notes and photos into clean proposals and one-click invoices. Move fast, document well, and you’ll cut call-backs and boost trust on every heating job.
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