Part of the giant physics experiment was turned off for the weekend while engineers probed a magnet failure.
But a Cern spokesman said damage to the £3.6bn ($6.6bn) particle accelerator was worse than anticipated.
The LHC is built to smash protons together at huge speeds, recreating conditions moments after the Big Bang.
Scientists hope it will shed light on fundamental questions in physics.
On Friday, a failure, known as a quench, caused around 100 of the LHC's super-cooled magnets to heat up by as much as 100C.
The fire brigade were called out after a tonne of liquid helium leaked into the tunnel at Cern, near Geneva.
Cern spokesman James Gillies said on Saturday that the sector that was damaged would have to be warmed up well above absolute zero so that repairs could be made.
While he said there was never any danger to the public, Mr Gillies admitted that the breakdown would be costly.
He said: "A full investigation is still under way but the most likely cause seems to be a faulty electrical connection between two of the magnets which probably melted, leading to a mechanical failure.
"We're investigating and we can't really say more than that now.
"But we do know that we will have to warm the machine up, make the repair, cool it down, and that's what brings you to two months of downtime for the LHC."
The first beams were fired successfully around the accelerator's 27km (16.7 miles) underground ring over a week ago.
The crucial next step is to collide those beams head on. However, the fault appears to have ruled out any chance of these experiments taking place for the next two months at least.
The quench occurred during final testing of the last of the LHC's electrical circuits to be commissioned.
At 1127 (0927 GMT) on Friday, the LHC's online logbook recorded a quench in sector 3-4 of the accelerator, which lies between the Alice and CMS detectors.
The entry stated that helium had been lost to the tunnel and that vacuum conditions had also been lost.
The superconducting magnets in the LHC must be supercooled to 1.9 kelvin above absolute zero, to allow them to steer particle beams around the circuit.
As a result of the quench, the temperature of about 100 of the magnets in the machine's final sector rose by around 100C.
The setback came just a day after the LHC's beam was restored after engineers replaced a faulty transformer that had hindered progress for much of the past week.
absolute a. 純粹的;完全的[B]
admitted a. 公認的,明白的
anticipate vt. 預期,期望;預料[+v-ing][+that][+wh-]
beam n. 樑;桁;(船等的)橫樑
brigade vt. 把...編成旅(或隊)
CERN n. Conseil European Pour Recherches Nucleaires 【法】歐洲核子研究委員會
circuit vt. 繞...環行
collide vi. 碰撞;相撞
commissioned a. 受委任的,服役的
crucial a. 決定性的,重要的[(+to/for)]
detector n. 發現者;發覺者
downtime n. 停工時間
experiment vi. 進行實驗,試驗[(+on/with)]
failure n. 失敗[U][(+in)]
faulty a. 有缺點的;不完美的
fundamental a. 基礎的;根本的,十分重要的[(+to)]
Geneva n. 日內瓦
giant a. 巨大的[B]
hadron n. 強子(由物質粒子的虧子所組成)
halt vi. 停止行進;停止;終止
helium n. 氦
hinder vt. 妨礙;阻礙[(+from)]
liquid a. 液體的;液態的,流動的
logbook n. 記錄冊
magnet n. 磁石
particle n. 微粒;顆粒[(+of)]
physics n. 物理學[J]
probe vt. 用探針(或探測器)探查,探測
progress n. 前進,行進
quench vt. 壓制(慾望等),抑制;解(渴)[(+with)]
recreate vt. (尤指在工作後)使得到消遣(或娛樂)
restored a. 精力恢復的,精力充沛的
setback n. 挫折;失敗;倒退
shed vt. 流出;流下
smash vt. 粉碎;打碎,打破[(+up)]
steer vt. 掌(船)舵,駕駛[O]
superconductive a. 超導電的
transformer n. 促使變化的(或人物);改革者
vacuum vt. 用真空吸塵器清掃[(+out)]