An E1 code means there's a serious air leak, so the pump keeps running to try to hold the pressure.
What to try
1. Refit the tap unit.
Take it off, then press it firmly back onto the keg with both hands. You should hear two clicks when it's properly seated. Check the beer line is fitted correctly while you're there.
2. Check the seal.
While the tap unit is off, look at where it meets the keg. Any dirt or debris caught between the two will let air escape. Wipe both surfaces clean and refit.
3. Try another keg.
If the code comes back after refitting, the keg itself may be the problem. Fit a different keg with a new beer line.
Still showing E1?
If the code is still there after changing the keg, get in touch. Let us know what you've tried and whether the code appeared with more than one keg.