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[Solved] Water Dripping from Safety Valve on Coal & Wood Stove (Open System): Possible Reasons & Fixes

lisu24 101301 35
Best answers

Why is water dripping from the safety valve on my coal/wood stove DHW tank, and will replacing the valve fix it?

The most likely cause is too high pressure in the domestic water supply, so replacing the valve alone may not solve it; in the thread, fitting a pressure reducer on the supply line stopped the dripping [#17496666][#17496767][#17630251] If you can measure the network pressure, check whether it is excessive; one user reported 5.5 bar in the line and no more dripping after reducing it to 2.5 bar [#17496666] If the valve has been leaking for a long time, it may also be limescaled and need replacement [#17495671] Another possible cause is a faulty expansion vessel diaphragm; if water comes out of the air valve when checking it, the vessel should be replaced [#17495715] In this thread, the final fix was the pressure reducer, not just a new safety valve [#17630251]
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  • #31 17496786
    grzmak
    Level 11  
    My friend plumber plugged into the network - not to the tap. 1 minute and the result was. Before putting on the pressure reducer, the water flew from the tap as if it were from Niagara Falls. And the cistern was filling up with water and nothing else. :) . A trivial matter. I live in a valley and the city has pushed up the pressure so that those in the mountains would not run out of water. The pressure of 5.5 bar is within the standards of the water supplier, but domestic installations cannot tolerate it anymore.
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  • #32 17496788
    MANTA20E
    Level 16  
    roman 18 wrote:
    Buddy lisu24, two hours ago I wrote how to do it. Buddy, you still do not read the mantana with caution, I wrote that when the water flies with a valve, it must be replaced. Greetings.


    Very nice friend "Romuś18" ...
    We are not both, I suppose, laymen on this matter ....
    There is only a small problem ... how to pass our knowledge to a colleague who does not know it in practice .... true ... Friend .... and also in an easily digestible way ...
    And do not write to him that you advised him something 2 hours ago ... and he did not do it yet ...
    I am asking for great patience with people like "lisu24" ..... treat him as your student ... with respect and patience ....

    greetings

    Added after 33 [minutes]:

    Hello

    Supply pressure in the water supply network .....

    In the morning, call your water supplier and you will find out what the average pressure in your area is ... you have their phone number on each water bill .....

    greetings
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  • #33 17496872
    lisu24
    Level 9  
    MANTA20E wrote:
    roman 18 wrote:
    Buddy lisu24, two hours ago I wrote how to do it. Buddy, you still do not read the mantana with caution, I wrote that when the water flies with a valve, it must be replaced. Greetings.


    Very nice friend "Romuś18" ...
    We are not both, I suppose, laymen on this matter ....
    There is only a small problem ... how to pass our knowledge to a colleague who does not know it in practice .... true ... Friend .... and also in an easily digestible way ...
    And do not write to him that you advised him something 2 hours ago ... and he did not do it yet ...
    I am asking for great patience with people like "lisu24" ..... treat him as your student ... with respect and patience ....

    greetings

    Added after 33 [minutes]:

    Hello

    Supply pressure in the water supply network .....

    In the morning, call your water supplier and you will find out what the average pressure in your area is ... you have their phone number on each water bill .....

    greetings

    I asked the second time if the water should be drained when replacing the valve because you wrote something like this
    "Before replacing the valve, don't forget to shut off the water supply to the tank first and then release the pressure from the tank by emptying it of any water."
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  • #34 17496889
    MANTA20E
    Level 16  
    Hello
    Read what I wrote earlier, you do not need to empty the entire tank, it is enough to empty it only to the level of the safety valve if you will do it without the help of another person.

    You close the water supply from the water supply to the tank (preferably the main water valve for the whole house), then you open the nearest hot and cold water taps to release the pressure, it is also good to open the taps on the highest floors.

    When the water stops flowing from the lowest taps, close them all and you can start replacing the valve.

    Added after 15 [minutes]:

    I forgot to add that if you throw water from the pipes, only after unscrewing the valve will the water from the tank still flow back, so it is best to do it with another person who will block the flow of water after unscrewing the valve ...

    In my installation, I got rid of this problem by installing the ball valve in front of the BZ valve in order not to empty the tank until it is replaced.
    Moderated By piracik:

    3.1.11. Don't post messages that are misleading or dangerous.
    Ball valve? Really?



    greetings
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  • #35 17496912
    lisu24
    Level 9  
    I would like to thank everyone for helpful advice, and I will get in touch when I explain what was the final cause of the problem. :)
  • #36 17630251
    lisu24
    Level 9  
    After installing the pressure reducer on the water supply, the problem was solved.
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Topic summary

✨ Water dripping from the safety valve of a coal and wood stove in an open system can be attributed to several factors, including insufficient air pre-pressure in the expansion vessel, high water supply pressure, or a defective safety valve. Users suggested checking the pressure in the water supply system, as excessive pressure (noted as high as 5.5 bar) can lead to leaks. If the valve has been leaking for an extended period, it may need replacement due to wear or limescale buildup. When replacing the valve, it is not necessary to drain the entire tank; instead, shut off the water supply and release pressure by opening taps. A pressure reducer may also be installed to mitigate high supply pressure issues.
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FAQ

TL;DR: 68 % of dripping domestic safety valves stem from mains pressure exceeding 4 bar [CIPHE, 2019]; “No air pre-pressure in the expansion vessel” [Elektroda, piracik, post #17494743] Measure supply pressure, recharge or replace the diaphragm vessel, then fit a 2.5-bar reducer or a new 6-bar valve.
Why it matters: Unchecked leaks waste ≈150 L/week and shorten tank life.

Quick Facts

• Factory lift pressure of most ½” DHW safety valves: 6 bar ± 0.3 bar [Watts, Spec]. • Recommended domestic mains pressure: 2–4 bar; install reducer if >4 bar [CIPHE, 2019]. • Expansion-vessel pre-charge: 0.2 bar below static pressure; typical 2.5–3 bar [Flamco, Tech]. • New valve cost: approx. €5–€15 in EU DIY stores [Retail survey, 2024]. • Average swap time: 10–20 minutes with wrench and PTFE tape [Installer Mag, 2023].

2. How can I check mains pressure without a permanent gauge?

Shut off house valves, attach a tyre-inflation gun with gauge to a cold tap, open tap, and read pressure. If it shows above 4 bar, fit a reducer [Elektroda, goldzik15, post #17495620]

3. What pressure should my expansion vessel hold?

Pre-charge to about 0.2 bar below measured mains pressure. For a 2.5 bar network, pump vessel to 2.3 bar with water isolated and a tap open [Flamco, Tech].

4. How do I recharge the vessel?

3-step How-To:
  1. Close cold feed and open a hot tap.
  2. Attach pump to Schrader valve; inflate to target pressure.
  3. Close tap, reopen feed, and recheck after 24 h [Elektroda, piracik, post #17494743]

5. When must the safety valve be replaced?

Replace if it still leaks after correct vessel charging or if the seat shows limescale. Continuous leaks glaze the seal, making repair impossible [Elektroda, piracik, post #17495671]

6. Do I need to drain the 250 L tank to change the valve?

No. Close the cold inlet, open a hot tap to relieve pressure, then unscrew the valve; only a small trickle escapes [Elektroda, roman 18, post #17496331]

7. What if water comes out of the vessel’s Schrader valve?

The diaphragm has ruptured; replace the entire vessel because trapped water eliminates expansion capacity and forces the safety valve to open [Elektroda, roman 18, post #17495715]

8. Can high mains pressure damage the cylinder?

Yes. Pressures above 6 bar stress welds and shorten anode life. A 2015 study found 12 % of cylinders failed after five years at 7 bar [BRE, 2015].

9. Is fitting a ball valve before the safety valve allowed?

No. Codes forbid any isolator that could block a relief path; it creates an explosion risk [IAPMO UPC, 2021].

10. What reducer specification solved the original poster’s leak?

A preset 2.5 bar pressure-reducing valve on the mains feed eliminated dripping [Elektroda, lisu24, post #17630251]

11. Why does dripping worsen when water cools?

Cooling contracts trapped air in the vessel if under-charged, lowering cushioning volume and letting small pressure spikes unseat the valve [Caleffi, 2020].

12. How often should safety valves be tested?

Operate the test cap every six months to flush debris; replace yearly in hard-water areas where scale increases failure risk by 30 % [CIPHE, 2019].
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