Before replacing a weeping pressure relief valve on a Navien boiler, a technician usually checks the expansion tank first, since that's the more common root cause.
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Quick answer
The pressure relief valve on a Navien boiler is a safety device that opens automatically if system pressure rises above a rated safe limit, discharging water to protect the boiler and connected piping from overpressure. When it's weeping under normal operation, the cause is frequently a waterlogged expansion tank pushing system pressure higher than it should be rather than a fault in the valve itself, so a technician typically checks the whole pressure system — not just the valve — before deciding what actually needs replacing.
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Every sealed hydronic boiler system, including Navien's combi models, operates within a designed pressure range, and the relief valve exists as a backstop in case something pushes pressure beyond that range unexpectedly — a failed expansion tank, an overfilled system, or another developing fault. It's rated to open at a specific pressure for your boiler and discharge water to bring the system back to a safe level before anything is damaged.
Because it's purely a safety component, it's built to fail toward safety, meaning a valve that starts weeping shouldn't be capped, plugged, or ignored — doing so removes the exact protection the valve is there to provide.
In a large share of service calls involving a weeping relief valve, the valve is actually responding correctly to genuinely elevated system pressure — most commonly because the expansion tank has failed and lost its ability to absorb the normal pressure rise during a heating cycle. Replacing the valve alone in that situation just delays the same symptom returning once the new valve is exposed to the same underlying overpressure.
That said, relief valves are wear items in their own right — mineral deposits can prevent a valve from reseating fully closed after it's opened even once, so a valve that discharged in the past can sometimes keep weeping afterward even once pressure is back to normal.
If the valve itself is confirmed faulty — or the root cause has already been addressed but the valve still won't seal properly — replacement involves isolating and depressurizing the affected section, removing the old valve, and installing a new one matched to the boiler's rated pressure. Discharge piping routing is checked at the same time to confirm it terminates at a safe location per code, since that routing matters if the valve is ever called on to actually discharge for a real overpressure event.
CANRO doesn't recommend manually testing a relief valve as a DIY step — lifting the valve to "check" it can sometimes prevent it from reseating properly afterward, which turns a minor concern into a valve that genuinely needs replacing.
When a relief valve does open, the discharged water needs somewhere to go that won't cause damage or create a hazard, which is why local plumbing code specifies how discharge piping from a relief valve must be routed — typically down and away from the boiler to a suitable drain or a visible, safe termination point where a discharge event would be noticed rather than hidden inside a wall cavity or ceiling space. Checking this routing is a standard part of any relief valve replacement, not just an afterthought.
On older installs, especially in homes that have had renovations done around the mechanical room, it's not unusual to find discharge piping that no longer meets current code, and a technician replacing the valve will typically flag and correct this at the same time.
Because a weeping relief valve is so often tied to the expansion tank, a service call for this symptom tends to become a broader look at the whole pressure and expansion system rather than a narrow single-part swap. That's a reasonable use of the visit, since these components genuinely work together, and addressing only the symptom you called about while ignoring a related root cause tends to bring you back to square one within a season.
A thorough technician will walk you through what they checked across the whole pressure system, not just what they replaced, so you understand whether the fix addresses the underlying cause or just the immediate symptom.
Safety note
If you see water actively discharging from the relief valve's piping rather than a light drip, or notice a gas smell, leave the home and call FortisBC at 1-800-663-9911 from a safe location. This repair should be handled by a licensed technician who can also confirm the underlying cause.
It's not usually an immediate emergency, but it shouldn't be left unaddressed either — it points to either a valve problem or elevated system pressure that's worth diagnosing before it worsens.
No — a pressure relief valve isn't meant to be sealed shut, and doing so removes an important safety function on a pressurized gas-fired system.
A technician typically checks the expansion tank's precharge first, since that's the more common root cause of elevated pressure leading to a weeping valve.
It's matched to your specific boiler's documented maximum safe operating pressure, not selected by guesswork or a generic standard part.
It's less common, but age and mineral exposure over time can still affect a valve's seat even without a prior discharge event.
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