The way most(not all) of those systems work is that there is a water pump that discharges to both an accumulator tank and the pipe that goes to the shower.
The accumulator will work using air-over-water hydraulic principles. Because liquids are not compressible, and gasses are, this will allow pressure to be built up and maintained inside the plumbing.
The pump is controlled by a pressure sensor on the accumulator. Quite simply, the pump only tried to maintain pressure in the accumulator. When the pressure drops, it turns on. Once the pressure reaches a preset level, it turns off.
The accumulator allows the system to maintain pressure. It serves exactly the same purpose as the tank on an air compressor. When water flows in under pressure, it will compress the air above it. In turn, the air will act like a spring, and provide pressure even when the pump stops. This also means you won't have to wait for the water to come through the pipes when you turn on the shower.
When you open the valve on the shower, pressure in the system drops, the pressure sensor will detects this, and turns the pump on. Pressure is also released from the accumulator.
When you turn the shower off, the pump should continue for a short time(probably about 1-5 seconds), while pressure builds up in the accumulator and trips the pressure switch.
HOWEVER, if the accumulator is flooded, pressure will never be able to really build up. The maximum pressure will be reached the minute the pump turns on, and even a tiny leak will release the pressure quickly.
A major leak will cause the same thing to happen even if the accumulator still has the correct air/water ratio.
I assume you would have noticed a major external leak in the system, so I'll rule that out.
The first thing I would check is to see if the accumulator is flooded. Turn off the pump, and very quickly open the water faucet. There should be a burst of water, which gradually stops. If the pump is mounted above the shower, this may happen regardless of the amount of air in the accumulator, but would also drain the accumulator.
-If no water comes out of the faucet with the pump off, the accumulator os probably completely flooded, and has no air to maintain pressure.
-If water DOES come out:
1) Leave the faucet open.
2) Re-enable the pump.
3) After the water flow starts again, close the faucet.
4) Wait to see if the problem persists.
If that didn't fix it, the problem is probably an internal leak.
Aside from an external leak, there are two ways water could escape from the system. The shower, and back down the intake pipe. There will be a check valve of some sort to prevent the water from travelling back down the intake pipe. You'll need access to the pump to check this.
On the pump there are three things you should check.
First, if easily possible, drain the accumulator to make sure it really does have air in it, then re-test the system.
Second, remove and examine the check valve. This will be a connector either on the pump's intake tube, or the output tube before the accumulator. Re-test the system.
Third, the pressure sensor sounds like it is working, since the pump DOES turn on, and turn off, but I'd check that if the above things don't help.
If none of those help, check again to make sure there aren't any external leaks. Then I'd call a plumber.
EDIT: I got some more info about those pumps, and the aqualisa pumps look like they may just use the waterline pressure rather than an accumulator to maintain pressure.
In that case, it could be that the water line pressure is too low, or the pump isn't set right.
[Edited by galacticroot on 06-01-2003 at 5:54 AM GMT]
