To repair a Moen shower valve that is either leaking or not balancing the cold and hot water correctly, begin by replacing the shower valve cartridge. A Moen shower valve cartridge has different working parts that malfunction with time. Replacing the cartridge can solve a number of problems.
Before removing the old cartridge, shut off the water to the house and turn on the faucet in the bathroom sink to drain any water remaining in the pipes.
Although a Moen cartridge puller is not necessary, it can make removing the cartridge easier.
Remove the faucet handle, the handle collar and adapter and the retention clip, in that order. Loosen and remove the cartridge to check for debris. Clean it as required, and insert the new cartridge. Reassemble it in reverse order.