Why Is Water Pressure So High All of a Sudden?

A sudden surge in residential water pressure represents a critical plumbing concern that demands immediate attention. This phenomenon manifests through symptoms ranging from persistent pipe noises to catastrophic system failures, with root causes spanning mechanical failures, Council supply fluctuations, and thermodynamic forces.

This article explains the main reasons why water pressure suddenly increases and offers practical solutions to fix the problem and avoid wasting water.

Before we start, we feel it’s important to get a little technical and explain the principles of residential water distribution.

Council water systems operate through gravitational potential energy stored in elevated tanks and towers, with standard residential pressure maintained between 45-80 PSI through pressure-reducing valves (PRVs). These systems balance static pressure (potential energy) and dynamic pressure (kinetic energy) through continuous flow regulation. The relationship between elevation differential (Δh) and pressure (P) follows:

P=ρgΔh

where ρ=water density and g=gravitational acceleration. Sudden pressure spikes disrupt this equilibrium, exceeding pipe tensile strength thresholds.

Professional plumbers utilise bourdon tube gauges to detect anomalies, with digital loggers tracking diurnal patterns. The Australian Standard AS/NZS 3500.1 mandates maximum 500 kPa (72.5 PSI) static pressure for residential installations. Transient surges during valve closures can momentarily exceed 1,000 kPa, risking joint failures.

According to plumbing insurance claims, faulty pressure-reducing valves (PRVs) are the foremost cause of sudden pressure spikes, responsible for 38% of residential cases. These brass-and-rubber assemblies degrade through:

1. Diaphragm Fatigue: Repeated flex cycles cause microtears in nitrile diaphragms, allowing uncontrolled upstream pressure transmission
2. Poppet Valve Erosion: High-velocity water erodes stainless steel valve seats, creating leakage paths that bypass regulation
3. Spring Creep: Constant compression reduces return force by 0.3% annually, gradually increasing setpoint pressure

A failed PRV allows full mains pressure (often 150+ PSI) into household pipes, evidenced by gauge readings exceeding 80 PSI. Replacement typically costs $220-$650 AUD, depending on valve size and accessibility.

In sealed plumbing systems with working pressure relief valves (PRVs), hot water expands and can create dangerously high pressure. Water expands by about 2.1% when heated from 15°C (59°F) to 65°C (149°F). If there’s no expansion tank to absorb this extra volume, the pressure can spike up to 150 PSI when the water heater is running. That’s why modern plumbing systems use thermal expansion control valves (TECVs) or expansion tanks with bladders to handle the increased water volume.

Sometimes, water companies like Sydney Water increase the water pressure in their pipes to supply large users like hospitals or fire hydrants. This can cause a jump of around 15 PSI in home water systems, unless the pressure relief valve (PRV) has a bypass to handle the extra pressure. People living near pumping stations are most likely to notice these sudden pressure increases.

When water flow suddenly stops (like when a valve slams shut), it creates powerful shockwaves called “water hammer.” These shockwaves can be strong enough to break pipes. For example, quickly closing a valve can create pressure spikes much higher than standard PVC pipes can handle, leading to leaks or bursts. Devices like air chambers or surge arrestors act like cushions to absorb these pressure spikes and protect your plumbing.

The Joukowsky equation quantifies surge magnitude:

ΔP=ρcΔv

Where c=wave speed (1200 m/s in copper) and Δv=velocity change. A 2 m/s valve closure creates 2400 kPa spikes – sufficient to rupture PVC joints rated for 1400 kPa.

Homes at the bottom of a hill have naturally higher water pressure due to gravity. For every 10 meters (about 33 feet) of elevation drop, the water pressure increases by about 14.2 PSI. If you live in such an area, the pressure-reducing valve (PRV) in your home may need to be adjusted yearly to account for changes in the underground water level. This can be a more common problem in areas such as the North Shore of Sydney and even parts of the Hills District.

Tree roots, especially from fast-growing trees like Ficus and Poplar, can grow into pipe joints and partially block the flow of water. This blockage acts like a bottleneck, forcing the water to speed up as it squeezes through. This faster flow can cause pressure to build up before the blockage, potentially leading to problems. A technique called “trenchless pipe relining” can fix these blockages without having to dig up the whole pipe.

While high water pressure itself isn’t a direct health risk, extremely high pressure (above 80 PSI) can damage safety devices (like Backflow Prevention Devices) that prevent contaminated water from backflowing into your clean water supply. This poses a risk of contamination through cross-connections. Because of this risk, health regulations require commercial properties to install pressure-limiting valves (PLVs). These valves are also becoming increasingly common in residential homes, especially in flood-risk zones, adding another layer of protection.

Plumbers usually employ one or more of the following testing methods for check for high water pressure:

1. Baseline Measurement: Attach gauge to laundry tap, record static pressure over 24 hours.
2. Thermal Test: Monitor pressure during water heater activation cycles.
3. Municipal Isolation: Shut off main valve; if pressure drops, fault lies upstream.
4. Regulator Bypass: Install temporary gauge across PRV to check differential.

Plumbers employ several methods to address high water pressure issues in residential plumbing systems:

The primary solution for high water pressure is adjusting or installing a pressure-reducing valve (PRV). Plumbers will:

1. Locate the pressure regulator near the main water shutoff valve
2. Loosen the locknut on the regulator
3. Turn the adjustment screw counterclockwise to decrease pressure
4. Test water pressure at different fixtures until the desired pressure is achieved

If no PRV is present, a plumber will install one on the main water line to regulate incoming pressure to a safe level, typically between 40-60 PSI.

To mitigate pressure fluctuations caused by water heating, plumbers often install expansion tanks near water heaters. These tanks absorb excess pressure, helping to stabilise overall system pressure.

In cases where high pressure is caused by constricted or damaged pipes, plumbers may recommend replacing pipes with larger diameter ones to improve flow and reduce pressure. This is a more extensive solution that involves replumbing work.

Fixing any existing leaks in the plumbing system can help normalise water pressure. Plumbers will locate and repair hidden leaks to ensure proper system function.

Professional plumbers use pressure gauges to accurately measure and test water pressure at various points in the system. They ensure pressure readings fall within the safe range of 55-60 PSI, addressing any readings above 70 PSI.

By implementing these solutions, plumbers can effectively manage high water pressure, preventing damage to plumbing fixtures and appliances while ensuring optimal system performance.

If you are experiencing high water pressure issues, give the friendly team at North East Plumbing a call today, we’d be glad to help!