Ferrari's Sebastian Vettel topped the times for the second day in a row at the opening test of the season in Jerez as McLaren again struggled and world champion Lewis Hamilton had his 2015 debut cut short by a water leak. Vettel improved on his Sunday time with a 1:20.984 before rain in the final hour ruled out any further quick laps. The Ferrari completed a total of 78 laps – another improvement on Sunday – and was lapping in the 1:23s on longer runs. His time was 0.883s clear of his nearest competitor Felipe Nasr, who continued Sauber's solid start to testing with 87 laps. Rookies Nasr and Max Verstappen in the Toro Rosso went out to get some wet weather experience in the final hour and were joined by some of their rivals as the rain eased ahead of the chequered flag. Mercedes had already called an early end to Hamilton's day after a technical problem resulted in a water leak on the W06. Initially the team had hoped to get him back out on track quickly, but the problem proved harder to resolve than it had hoped. Nevertheless, Hamilton still registered 91 laps in total – shy of team-mate Nico Rosberg's mammoth 157 on Sunday, but still more than any other team managed on Monday. Red Bull also hit trouble, limiting the RB11's mileage for the second day in a row. On Sunday the team had power unit related problems but on Monday it was down to driver error. On his debut with the team, Daniil Kvyat made a mistake on a cold track and nudged the barriers – skewing and damaging the front wing. With the pre-season just over a day old, Red Bull did not have a replacement at the track and had to remove the wing completely to allow him to continue to run. In total he notched up 18 laps, but was limited to practice starts at the end of the pit lane and therefore did not set a lap time. The team is having a replacement wing flown in to allow it to resume a proper test programme tomorrow. Once again the McLaren-Honda was a rare sight on track and Jenson Button could only add six laps to match Fernando Alonso's tally from day one. The team is struggling to get the new power unit communicating with the other systems on the car and the result was a lap 33 seconds off the pace. In its current state the Honda's exhaust note is noticeably louder and throatier than its rivals, but it has yet to run smoothly or at high revs to make a fair comparison. McLaren hoped to get the car on track soon after lunch for more mileage, but despite several fire-ups it only emerged from behind the screens covering the garage door in the last 20 minutes of the day to add one extra lap to the morning's five. After receiving delivery of its car yesterday from the factory and building it overnight, Lotus made its 2015 debut in the second hour of running with Pastor Maldonado at the wheel. He went on to complete 41 laps but caused a red flag towards the end of the session. Lotus later confirmed the E23 had been curtailed by a drivetrain issue. Williams had a solid if unspectacular day as Valtteri Bottas set a best time of 1:22.319 and completed 61 laps while Verstappen managed 73 in the Toro Rosso and a best time of 1:24.167.