If your tenant is behind in the rent, you cannot do anything that affects the supply of utilities, as this would be an offence under the Residential Tenancies Act, and would allow the tenant to take you to the Landlord and Tenant Board for a rent abatement.

You should serve the N4 in the proper manner, giving 14 days for the tenant to pay or move out, and then file an L1 application with the Board on or after the 15th day.