I've just moved into a new house and the heating doesn't work, hot water isn't circulating. I've narrowed it down to a stuck valve on the inflow to the water pump, it seems that the valve is closed. Unfortunately the thread on the valve has been worn down, so the usual tools can't attach to it (see pic).

Brute force with a spanner doesn't work, even after applying a lot of oil. I want to try gently heating it to see if that loosens things. Do any of you have some other tips or tricks that might help loosen it? I'm pretty good at home improvement but this one has me stumped... Stuck valve with worn thread

  • If you can't open it with a pair of pliers, it might be because it's already open. Have you tried to close it instead? Are you sure it's the valve? What did you do that narrowed it down to the valve? Nov 22, 2018 at 11:04
  • I'm sure it's the valve, and I have tried turning it both ways, yes. There is only about 80 degrees of travel in the valve. The valve on the pump outflow (same type) has 5 whole revolutions of travel.
    – os1
    Nov 22, 2018 at 11:19
  • Did you try to loosen the small packing nut on the stem and then turning the stem?
    – d.george
    Nov 22, 2018 at 13:10

2 Answers 2


Heat is an option, just note that if the valve seats with any kind of polymer/rubber seals you'll likely destroy them. In my experience, heat is never gentle if it's going to be effective.

I'd go for heat first (like acetylene-hot, not that weak propane/mapp hot), but be VERY ready to have to go out and replace the whole valve.

From looking at your picture, I'd cut above the 90 degree bend and sweat in a new bend and valve. After all, you're going to want to open and shut the valve at some point in the future, if you deal with it now, you'll be thankful later.

  • Thanks, in the end we replaced the entire heating system - so the stuck valve wasn't an issue!
    – os1
    Dec 13, 2018 at 13:52

Before you cut the copper to replace the valve, see if you can close the other valve and loosen the pump slightly (as if you were going to remove it), just to allow the water to flow slowly. If only a small amount of water comes out and stops leaking then you can assume the stuck valve is really closed. If the valve is stuck closed, you could look into the valve to see how the valve is constructed. My guess is that it is a gate valve. If it is a gate valve, they tend to stick from something stuck in the gate or the seat or from pressure on the upstream side of the valve. If that is the case, reduce the water pressure in the system as low as you can by opening a drain valve on the boiler and leaving all the vent valves closed. This can put the system into a slight negative pressure. You are trying to relieve the pressure on the inlet side of the valve. Then try turning the valve open (CCW). The last thing to try would be to have a 2nd person hid the gate inside the valve with a hammer and chisel or drift punch while you try to turn the valve open.(CCW) These are things I have done to open stock gate valves. Hope this helps.

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