London System traps: 6 mistakes at 1400-1600 Elo

October 9, 2026 · 4 min read

At 1400-1600 both sides know the London setup. White plays d4, Bf4, e3, Nf3, c3 and Bd3; Black copies with ...Bf5 or ...Bg4 and waits. The mistakes come from diagonals. A pawn move opens a line to the queen or the rook, or a piece that was guarding something quietly leaves.

We took the Lichess blitz and rapid games from August 2026 where both players were rated 1400 to 1600, followed the London move by move, and had Stockfish check every position where many players took the same wrong turn. Every line below was verified by the engine. All six examples are told from White’s side. For the main ideas of the opening, read our London System guide. One level down, see 6 mistakes at 1200-1400 Elo; one level up, 6 mistakes at 1600-1800 Elo.

Part 1: punish it

Three Black mistakes, three punishments. Each time Black weakens a line or a square, and one White move is enough to use it.

1. 6...b6, and the long diagonal opens

After 1.d4 d5 2.Bf4 Nc6 3.e3 Bf5 4.Nf3 e6 5.c3 Nf6 6.Qb3, the queen hits b7. 26% of Black players guard it with 6...b6. But the pawn on b7 was also shielding the rook on a8. 7.Bb5! threatens 8.Bxc6+, with check, and then 9.Bxa8. After 7...Be7 8.Bxc6+ Kf8 9.Bxa8 Qxa8, White has won a knight and a rook for the bishop. 10 of the 11 White players who faced it found 7.Bb5.

Black should play 6...Rb8 instead, as 44% did, and the game is balanced.

6...b6? and 7.Bb5! wins a rook.

2. 4...Ne4, and the bishop on f5 loses its shield

After 1.d4 d5 2.Bf4 Nf6 3.e3 Bf5 4.Bd3, White offers the bishop trade. 6% of Black players block the diagonal with 4...Ne4 instead. 5.f3! kicks the knight, and the bishop on f5 is hit again. After 5...Nd6 6.Bxd6 Bxd3 7.Bxc7! Qxc7 8.Qxd3, White is a pawn up. If 5...g5, 6.fxe4 wins a piece. Only 35% of White players found 5.f3.

Black should trade with 4...Bxd3 5.cxd3, and the game is balanced.

4...Ne4? and 5.f3! wins a pawn.

3. 4...e5, and the d-file opens for White

After 1.d4 Nf6 2.Bf4 d6 3.e3 Nc6 4.Nf3, 19% of Black players push 4...e5. 5.dxe5! hits the knight on f6. If 5...dxe5, 6.Qxd8+ Kxd8 7.Nxe5 wins a pawn, and the black king has lost the right to castle. After 5...Nh5 6.Bg5 Qd7 7.exd6, White is two pawns up. Every White player in our sample found 5.dxe5.

Black should play 4...Nh5 instead and go after the bishop on f4. The game is balanced.

4...e5? and 5.dxe5! wins a pawn.

Part 2: avoid it

Now the White mistakes that come up most in the London at 1400-1600. In all three, White plays a natural move and forgets what the moved piece or pawn was guarding.

4. 3.e3 against 2...Bg4

After 1.d4 d5 2.Bf4 Bg4, 10% of White players play the usual 3.e3. But the pawn on e2 was the only thing between the bishop on g4 and the queen on d1. 3...Bxd1 wins the queen for a bishop. 17 of the 18 Black players who got the chance took it.

Play 3.Nf3 instead. The knight blocks the diagonal, and e3 can come next. 3.h3 also works, and is the most popular move here.

3.e3?? and 3...Bxd1. Play 3.Nf3 instead.

5. 5.h3 when d4 needs the knight

After 1.d4 d5 2.Bf4 c5 3.e3 Nc6 4.Nf3 Bg4, 23% of White players ask the bishop with 5.h3. But Black simply takes: 5...Bxf3 6.Qxf3 cxd4 7.exd4 Nxd4. The knight on f3 was guarding d4, and now the pawn falls with the knight hitting the queen. Black is a pawn up.

Play 5.c3 instead. Support d4 first, and the game is balanced.

5.h3? and 5...Bxf3! Play 5.c3 instead.

6. 7.Nbd2 with a knight on e4

After 1.d4 d5 2.Bf4 Nc6 3.e3 Bf5 4.Nf3 e6 5.c3 Nf6 6.Bd3 Ne4, 45% of White players develop with 7.Nbd2. It looks like the most normal move in the London, but the knight on b1 was guarding c3, and on d2 it cuts the queen off from d3. 7...Nxc3! 8.bxc3 Bxd3, and the bishop on d3 cannot be taken back. Black is a pawn up and White cannot castle. None of the 14 Black players in our sample found 7...Nxc3, but the engine is clear.

Play 7.Qc2 instead. The queen guards c3 and d3, and the game is balanced.

7.Nbd2? and 7...Nxc3! Play 7.Qc2 instead.

What to take away

When b7 or e2 moves, look down the diagonal behind it: a rook or a queen may be sitting there.
A knight that blocks a bishop trade can be kicked with a pawn, and the trade comes back with interest.
If Black pushes ...e5 with the queen on d8 and a pawn on d6, dxe5 opens the d-file for your queen.
Before moving a piece in the London, ask what it was guarding: the knight on f3 guards d4, the knight on b1 guards c3.

These patterns come from many games between players at your level, not from a theory book. Your own games have patterns too, and they are probably not the same ones. Chess X-Ray finds the moves where you lost your advantage in your chess.com or Lichess games, groups them by opening, and turns them into lessons you replay until they stick.