This is the most common cause. Check how the timer actually works:

• It starts within the hour you choose, not on the minute. To save power the unit sleeps and wakes every 30 minutes by default. A 7am setting starts at the first wake after 7:00, which could be up to half an hour later.
• Midnight can't be used. Choosing "-" in the app, or 0 on the unit, turns that slot off. The app offers 1am to 10pm; 11pm can only be set on the unit.
• "Every 2/3/…/7 days" follows the calendar date, not the last watering. For example, "every 2 days" waters on even dates, and "every 7 days" waters on the 7th, 14th, 21st and 28th. Near the end of a month the gap can be longer than you expect (up to 10 days with "every 7"). The app offers up to every 5 days; the unit's screen offers up to every 7.
• Days set to OFF ("Timer off" in the app), or a duration of 0:00, means that zone never waters on the timer.
• Two times in the same hour, or one hour apart: the second one is skipped or starts late. A zone won't water by timer if it watered in the previous hour. Keep Time 1 and Time 2 at least two hours apart.

By default the unit won't pump below 8°C to protect the pump and pipes from ice. On cool mornings in spring and autumn the timer is skipped, and that watering counts as done, so it won't try again later in the day.

• Signs: the Manual watering screen shows "Too cold to pump!". The app log shows "Too cold, not turning on".
• Fix: move the watering time to a warmer part of the day, or lower Min. pumping temp (0–15°C) under System setup on the unit, or "Don't water below" under Other watering settings in the app. Manual watering ignores this limit.

When the battery falls below about 20%, the unit stays on but stops pumping until the battery recovers above about 30%. Skipped waterings count as done.

Every unit runs on its internal battery. The battery is charged through the solar panel port, by either a 10W solar panel or a trickle charger, at up to 1 amp. Watering uses power much faster than that. Most waterings are short and the battery soon recovers. A long watering of around 10 minutes is rare, but long waterings, or several zones watering one after another, can drain the battery faster than it recharges. With a solar panel, low battery is common in winter, in shade, or when the panel is dirty or badly angled.

• Signs: a low-battery tone, and a "Low battery" event in the app.
• Fix: with a solar panel, clean it, angle it to face the sun (due south in the UK) and remove any shade. With a trickle charger, check it's plugged in and switched on. Shorten watering durations so each run uses less battery. If a solar panel can't keep up, a trickle charger plugged into the solar panel port keeps the battery charged in any weather.

Any watering in the hour before a scheduled time causes the timer to skip. This includes manual watering, a boost from the app, hot-weather boost, interval watering or sensor-triggered watering.

• Fix: check the zone's "last watered" time. Avoid manual runs just before a scheduled slot.

• The tank is empty or the pump is above the waterline. If the low water alarm is on, you'll hear the siren.
• The pump has an airlock or the inlet filter is blocked.
• Fix: refill the tank, prime the pump and clear the filter.

Pro pump: when its pressure switch cuts out, the pump draws almost no current, and the unit can mistake this for a pump running dry. With the low water alarm on, the siren can sound and the screen can show "Low water! Check pump / tank" even though the tank is full. Watering carries on. If the tank has water and the outlets are restricted, this is the pressure switch, not low water. To turn it off, set Low water siren to Off in the zone's settings in the app, or Low water alarm to 0 on the unit.

• After the battery went completely flat or the unit lost power, the clock may be wrong until the unit next connects online. A unit with a faulty internal clock won't water by timer at all until it gets the time from the internet.
• After the clocks change (BST/GMT), an offline unit keeps the old time, so it waters an hour early or late.
• Fix: check the time on the home screen. Connect the unit online once so it sets its clock automatically.

Outside the UK: the unit and the app currently work in UK time (GMT, or BST in summer). The unit sets its clock to UK time every time it connects, so changing the clock to your local time won't last. Set your watering times in UK time instead. For example, if you're one hour ahead of the UK and want to water at 7am local time, choose 6am.

The unit only checks in when it wakes (every 30 minutes by default). If it's offline (weak WiFi or mobile signal, changed WiFi password, SIM problem), changes made in the app never arrive. If you change settings on the unit and in the app at around the same time, one change can overwrite the other.

• Fix: check the zone settings on the unit's own screen. They are what actually runs. Press a button to wake the unit and make it check in.

A kinked or blocked hose, a closed tap or valve on the outlet, a frozen pipe or a jammed pump makes the pump strain. With high current shutdown turned on (the default; see High current shutoff under System setup on the unit), it stops after about 2 seconds.

Pro pump: the Pro pump has a pressure switch. When the outlets are closed or restricted, it switches off at high pressure and back on as pressure drops. This cycling is normal. As pressure builds towards the cut-out point, the pump draws more current. If it reaches the high current limit before the pressure switch cuts out, the unit stops watering as if there were a blockage. The Mini pump has no pressure switch, so on a Mini pump high current always means a blockage or a jammed or failed pump. Often this is a rusted motor, which is only resolved by a new pump. You can check by trying to rotate the vane (paddle wheel) from inside using a small screwdriver.

• Signs: a 2-second low tone, "Pump fault : high current" on the home screen, and very short watering.
• Fix: clear any blockage and check that every outlet is open. On a Pro pump with no blockage, you can lower the system pressure by adding more emitters, creating a loop, or creating a return feed to the water source.

The unit detects no pump current: the pump is unplugged, the cable is damaged, or the pump has failed. The valve still opens and the timer still runs, so this shows up as "the timer ran but nothing happened".

• Signs: "Pump fault : not connected?" on the home screen.
• Fix: check the pump connector and cable, and test the pump with a manual run.

• Built-in zones 1 and 2: a stuck solenoid, damaged wiring, or a valve wired the wrong way round. See Valve polarity below.
• Wired add-on valves (zones 3–6): if a valve controller was unplugged or lost contact, the zone can be dropped. When it reconnects it may be assigned a different zone number, and that zone has different (or no) schedule settings. Check the Wired devices page on the display screen.
• "Run pump" set to No on the unit, or "Turn pump on as well as valve" switched off in the app (shown as "Valve only"), means only the valve opens. That's correct for mains-pressure or gravity setups, but nothing will come out if you rely on the pump.

Valve polarity (zones 1 and 2): the built-in valves are opened and closed by a short electrical pulse, and the direction of that pulse matters. If a valve is connected the wrong way round, it closes when it should open and opens when it should close. You'll see no water when the zone should be watering, or water running when it shouldn't. A manual watering run is a quick way to check.

To reverse the polarity in software:

1. Wake the unit and connect your phone to the unit's own WiFi network (harvst-xxxx).
2. Open http://192.168.4.1/advanced
3. Set Valve 1 polarity or Valve 2 polarity to Reversed and tap Save. Turn the unit off and on again for the swap settings to take effect.

This needs the right firmware for your control unit:

• Control units without a screen: firmware from July 2025 onwards.
• Control units with a screen: firmware version 2026110500 or later. You can see the version under System info on the unit.

If your unit doesn't show the polarity settings, contact support.

An old battery may show OK at rest but drop sharply when the pump starts. If the voltage drops too far during watering, the unit stops the pump, plays a falling tone and shuts down, so watering is cut short. Other signs are frequent "low battery" skips despite good sun or a connected trickle charger.

• Fix: if the battery is several seasons old and shows these symptoms, replace it. If you're not sure, contact support.

Below about 10%, the unit plays a falling tone and sleeps for 24 hours without watering or connecting. It looks completely dead.

• Fix: it recovers once the solar panel or trickle charger has recharged the battery.

The unit can't read the temperature, so frost protection and hot-weather boost stop working. Waterings are then not skipped when they should be, or extra waterings don't happen.

• Fix: if the home screen shows "Temperature sensor fail / missing", check the sensor cable and plug. Otherwise check the temperature it shows is sensible.

This is normal. To save battery, the unit sleeps between check-ins (which happen every 30 minutes) with its screen off, and wakes on its own to water and report. It looks switched off, but it is still running its schedule.

• Fix: press ENTER. You'll hear a rising tone and the screen comes on. The unit stays awake for 5 minutes after the last button press.

The unit is awake (it beeps when you press buttons) but the screen is blank or not responding.

• Fix: hold UP and DOWN together for 3 seconds, then let go. You'll hear a beep at 2 seconds and the screen restarts after you release.
• Warning: don't keep holding. After 10 seconds the unit does a factory reset and erases all your settings.

Nothing happens at all: no tone when you press ENTER, even after a sunny day or with the trickle charger connected. If the unit is actually off rather than just asleep, you need to turn it on first with the power button.

• Fix: check the solar panel or trickle charger is plugged firmly into the solar panel port and its lead is undamaged. You can see whether the unit is charging on the System info screen: a working solar panel will show a voltage, and the charge current can go up to 1 amp in full sun with a low battery.
• With a trickle charger, also check it's plugged in and switched on at the wall. If the unit still doesn't respond, contact support.