Pool pump and filter problems: symptoms and what they usually mean

How the system fits together

Water leaves the pool through the skimmers and the main drain, passes through a strainer basket at the pump (often called the hair and lint pot), is pushed through the filter, then through any heater or chiller, and returns to the pool through the inlets. Dubai Municipality's plan approval guideline expects the filtration drawings for a pool to show the valves, inlet points, air release valve, pressure gauge, sight glass and sampling taps, which gives a good idea of what a properly equipped plant room contains.

Most pump and filter problems announce themselves through two things you can see without tools: the pressure gauge and the pump basket.

Reading the pressure gauge

Pentair's cartridge filter manual calls the pressure gauge the primary indicator of how the filter is operating. It asks owners to write down the original starting pressure after the filter has been cleaned, and to clean the cartridge when the reading is 8 to 10 psi higher than that figure. Your own filter's manual gives the figure for your model; the habit of recording the clean reading is what matters.

The same manual explains how to check the gauge itself. It should read zero when the system is off and pressure has been relieved, it should show pressure when the system is running, and it should be replaced if it does neither.

Pressure rising steadily

This is normal. The filter is holding dirt and needs cleaning or backwashing.

Pressure still high after cleaning or backwashing

Hayward lists several causes for a sand filter that stays at high pressure after backwashing:

• Clogged sand. Mineral deposits or other material that backwashing will not remove. Hayward notes that some calcium-based chlorines and alternative sanitisers can cause build-up in the sand bed, and suggests replacing the top layer of sand before replacing it all.
• A partly closed valve on the return piping.
• A pump that is too small. If it delivers less than 60 percent of the filter's design flow, the filter will never backwash fully.
• A pump that is too large. Flow above the filter's maximum causes excessive back pressure and, over time, channelling through the sand, which lets debris bypass the filter.

Pressure lower than usual

Pentair's troubleshooting advice is to check the skimmer basket and the pump basket for debris first. If they are clear, the next suspects are a clogged impeller in the pump or an obstruction in the line between the pool and the pump.

Air in the system

Air is a common cause of poor circulation. Pentair lists these signs:

• air bubbles, or a low water level, in the pump basket
• air bubbles coming out of the return inlets while the pump runs
• air spitting from the filter's air relief valve when it is opened with the pump running

And these usual causes:

• a low water level in the pool, so the skimmer starves for water
• a clogged skimmer basket
• a split suction cleaner hose
• a leaking pump lid
• a leak in the pump suction line

A leak on the suction side often draws air in rather than dripping water out, which is why bubbles in the pump basket are such a useful clue. A pump that struggles to prime, or loses prime, is usually suffering from the same causes.

Filter types and what each needs

Sand filters

Cleaned by backwashing: the flow is reversed to lift the trapped dirt out of the sand and send it to waste. When backwashing no longer restores the clean pressure, the media is due for attention.

Glass media

Some sand filter vessels are filled with crushed glass instead of sand. Manufacturers such as Dryden Aqua make this media from recycled glass bottles and market it for use in sand filters. A specialist will confirm that the media and your filter vessel are compatible.

Cartridge filters

Cartridges are removed and washed rather than backwashed. Pentair notes that frequent short cleaning cycles are normal after a pool is first filled, because fine dust from new plaster finishes loads the cartridge quickly.

Diatomaceous earth filters

Dubai Municipality's plan approval guideline lists diatomaceous earth filters alongside sand filters. They use a fine powder coating on internal grids and need their own cleaning and recharging routine from the manufacturer's manual.

Safety first

A filter is a pressure vessel. Pentair warns that before opening one you must switch off the pump, open the air relief valve and wait until the gauge reads zero. Never open a filter lid or clamp under pressure. Switch off the power before touching a pump, and leave electrical faults, including a tripping breaker, to a qualified specialist. Dubai Municipality requires each electrical circuit in a pool installation to have an earth leakage circuit breaker.

When to call a specialist

• pressure stays high after cleaning or backwashing
• bubbles in the pump basket continue after you have checked the water level, baskets and lid
• the pump will not prime, hums without running, or trips the power
• you see water leaking at the pump, filter or valves; the City of Scottsdale notes that most pool leaks are found at the equipment
• the filter is old and you are unsure whether the media or cartridge needs replacing

Note the clean and current gauge readings and photograph the equipment labels before the visit.