Care & maintenance
Do I need an external pressure tank with my pump?
A variable-speed pressure pump has a small pressure tank built in, and for most homes that’s all it needs. An external tank adds a bigger cushion of stored water. It won’t fix everything, but in a few setups it makes a real difference, and there’s one thing worth checking before you buy one.
What the built-in tank does
Inside the pump is a small pressure tank: water on one side, a cushion of air on the other. It covers the moment between a tap opening and the pump speeding up, and it holds pressure once the tap closes so the pump can stop.
An old on/off pump needed a big tank to stop it starting every few seconds. A variable-speed pump changes speed to match what you’re using, so it gets by with a much smaller one.
Check the built-in tank first
If the pump keeps turning on and off and you’ve looked for a leak without finding one, check the air in the pump’s own tank before anything else. The air slowly escapes over time, the cushion shrinks, and the pump starts and stops more than it should.
- Switch the pump off at the power and open a tap to bring the water pressure down to zero.
- Find the air valve on the tank. It’s the same kind of valve as a car tyre.
- Check it with a tyre gauge. It should sit at about 70% of the pump’s set pressure: for a pump set to 3 bar, about 2.1 bar.
- If it’s low, top it up with a tyre pump, restore power and watch whether the cycling settles.
If the tank won’t hold air
Water coming out of the air valve means the bladder inside has failed and the tank needs replacing. Our guide to re-pressurising a pressure tank goes through the check in more detail.
When an external tank helps
- Long pipe runs. On a big block, or where the pump sits a long way from the house, a larger cushion at the pump smooths out surges and gives the pump more to work with.
- Cycling you can’t trace. If the built-in tank is charged and there’s no leak you can find, a larger tank stores more water between starts, so the pump starts far less often.
- A dip in flow before the pump catches up. When a tap opens, the pump needs a moment to sense the drop and speed up. If you notice the flow sag first, a larger tank supplies water from storage during that moment and the flow stays even.
Fitting one
- It goes on the outlet (pressure) side of the pump, close to the pump.
- Set its air pre-charge to about 70% of the pump’s set pressure, with the tank empty of water. That’s the same rule as the pump’s own tank, so the two share the work.
- A plumber can size it for your pipe run and how your household uses water.
- Connecting anything to your home’s drinking water plumbing is work for a licensed plumber.
Safety: Switch off the pump’s power and release the water pressure before checking or adjusting a tank’s air charge. Don’t inflate a tank beyond the pressure marked on it.
How a Grewa Boost pump fits in
A Boost pump has a pressure tank built in, pre-charged at the factory, and runs at variable speed, so most homes need nothing else. If you change the set pressure a long way, reset the tank’s pre-charge to about 70% of the new setting, as the manual describes. And if the pump keeps nudging on overnight when nothing should be running, the app flags the pattern of a slow leak, which is worth ruling out before adding a tank.
Common questions
Will an external tank make my pump last longer?
If it’s cycling, yes: fewer starts means less wear. If it isn’t, a variable-speed pump already runs gently and a tank adds little.
Can a bigger tank hide a leak?
It can make one harder to notice, because the pump starts less often. Find and fix a leak first. A tank is for setups that need the extra cushion, not a cover for a drip.
What pre-charge should an external tank have?
About 70% of the pump’s set pressure, set with the water side empty. It’s the same rule as the pump’s own tank.