Legal Question in Landlord & Tenant Law in California

"Fixed it"? Is too ambiguous a term. The contract says "repair" which is what matters here. Thus ask yourself what did the plumber do.

The contract covenant for a tenant to repair (what you cited in your question) is interrupted by the court's not to create an undue burden of improvement on a tenant. Thus "Repair" means a tenant is to maintain the systems that currently exists and not the creation of something new. Meaning a repair is not a restoration. For example replacing old broken pipes that have worn out because of age with a new pipe is a restoration and not a repair. But patching the pipe is a repair not a restoration.

Thus did the plumber improve the condition of the property (condition when you got it) with a restoration (new pipes for example) or did you repair it by maintaining what you had gotten initially?

Generally Landlords are reponsible for repair that deal with inhabitability. There are specific provision for the repair and deduct method under California law

Here is some info from California Dept of Consumer Affairs

The "repair and deduct" remedy allows a tenant to deduct money from the rent, up to the amount of one month's rent, to pay for repair of defects in the rental unit.156 This remedy covers substandard conditions that affect the tenant's health and safety, and that substantially breach the implied warranty of habitability.157 (See discussion of the implied warranty of habitability.) Examples might include a leak in the roof during the rainy season, no hot running water, or a gas leak.

As a practical matter, the repair and deduct remedy allows a tenant to make needed repairs of serious conditions without filing a lawsuit against the landlord. Because this remedy involves legal technicalities, it's a good idea for the tenant to talk to a lawyer, legal aid organization, or tenants' association before proceeding.

The basic requirements and steps for using the repair and deduct remedy are as follows:

1. The defects must be serious and directly related to the tenant's health and safety.158

2. The repairs cannot cost more than one month's rent.

3. The tenant cannot use the repair and deduct remedy more than twice in any 12-month period.

4. The tenant or the tenant's family, guests, or pets must not have caused the defects that require repair.

5. The tenant must inform the landlord, either orally or in writing, of the repairs that are needed. (See "Giving the landlord notice".)

6. The tenant must give the landlord a reasonable period of time to make the needed repairs.

What is a reasonable period of time? This depends on the defects and the types of repairs that are needed. The law usually considers 30 days to be reasonable, but a shorter period may be considered reasonable, depending on the situation. For example, if the furnace is broken and it's very cold outdoors, two days may be considered reasonable (assuming that a qualified repair person is available within that time period).

7. If the landlord doesn't make the repairs within a reasonable period of time, the tenant may either make the repairs or hire someone to do them. The tenant may then deduct the cost of the repairs from the rent when it is due. The tenant should keep all receipts for the repairs.

It's a good idea, but not a legal requirement, for the tenant to give the landlord a written notice that explains why the tenant hasn't paid the full amount of the rent. The tenant should keep a copy of this notice.

I will also note that landlords and tenants can contract that the tenant is responsible for all repairs in exchange for a reduced rent amounts...but it had to be ingood faith and you have ability to pay...