Water heaters are the hardest working and most unnoticed appliances in every household – until they start leaking.
Drips and leaks often come from your water heater’s temperature and pressure relief valve. Unfortunately, replacing only the temperature and pressure relief valve is usually not the best solution for homeowners.
A water heater has three critical components, each impacting the performance of the others. Here is how we diagnose what is going wrong and why we often recommend replacing all three parts at once versus trying to solve the problem piecemeal.
The Temperature & Pressure (T&P) Relief Valve?
The temperature and pressure (T&P) relief valve is usually on the side or top of the water heater and piped to the pan or a nearby drain. It is your water heater’s safety device. It is designed to release water to protect the heater when pressure exceeds 150 psi or the temperature exceeds 210°F. Once the T&P valve trips, it always needs to be replaced.
If your water heater’s temperature exceeds 200°F, we usually have no reason to investigate further. It is time for a new water heater.
Otherwise, the T&P leak may be caused by an issue with the expansion tank, the pressure-reducing valve, or both.
NATE SAYS: Water heater manufacturers recommend testing the T&P valve annually, but there’s a catch: testing it can cause it to trip, and once tripped, it may not reseal properly, leading to nuisance drips. Since the T&P relief valve is a critical safety device, it should never be capped.
The Expansion Tank
The expansion tank is roughly the size of a basketball and is above the water heater. It has an air-filled bladder that compresses to allow the water to expand as it heats.
If the expansion tank fails, there is no room for the water to expand, increasing pressure on your water lines and often causing the T&P valve to trip. When the expansion tank is faulty, water can enter the bladder, preventing it from compressing. Since water does not compress, this can lead to pressure issues.
The only good way to test the expansion tank is to remove it and ensure it’s not holding water. We all know that once removed, plumbing sometimes doesn’t work right when reinstalled.
So, to avoid leaks or worse, we recommend replacing the expansion tank rather than reusing a potentially compromised one.
The Pressure Reducing Valve (PRV)
The pressure-reducing valve (PRV) is typically located where water enters your home. It ensures that the pressure from the street is reduced to a safe level, preventing the T&P valve from tripping due to high pressure.
If your PRV valve is faulty, it will often blow the bladder in your expansion tank.
However, diagnosing a faulty PRV is challenging for two reasons:
- During the day, pressure may be lower and within the safe limit of 80 psi, but with less usage in the neighborhood, pressure can rise to damaging levels at night.
- Testing the pressure on the inlet side of the PRV is often impossible without installing gauges and test ports, which could cost more than a new PRV.
Three Components, One System
T&P relief valve leaks are the most common leaks we see as plumbers. We hope this article helps homeowners understand how all three critical components work together as a total system. When we recommend replacing all three elements, it’s not because we are trying to upsell you. It saves you time and money in the long run and ensures your water heater works safely and correctly.