Dear MYaqoob,
Disclaimer : Although the people in this forum may have warm voices, wear blue glasses, colorful clothing and softly whistle "don't kill the world" on their way to the trainstation - answers here is not a replacement for getting professional support :
Step 0 : (seriously consider to)
i-Join a "Mieterschutzverein" (possible online) (Generally 2 year membership, join fee =15€ once-off, 5,75€ per month (prices vary).
ii-Or get a lawyer (if you have legal insurance but forgot to mention this up till now the insurance is often void anyway. Legal fees tables for that depends on the size of the claim - reckon with nothing less than 1100€. if you loose, you have to pay his/her laywer also.
Anyway be prepared to answer the following
A) Was any of these additionally points stated on the contract, or, for that matter, on a letter countersigned by both parties?
B) Do you have
i) any formal written proof of your complaints / in the presence of another objective party or
ii) was it all verbally / via the telephone/ ?
Otherwise it is possible to claim that he was unaware /you didn't clearly communicate.
3) Before you start with step a) or b) You have to give a landlord sufficient time to correct his obligations, with the clock starting to tick only after formally (ie letter) documenting your complaints (Einwurf-Einschreiben oder Einschreiben mit Rückschein).
Ideally you documented all deficits on the first day with photos. Photo-copies should be included. Note everything, 1mm scratches, loose screws, unfinished painting, 3mm water spots on floors, scratches on taps/ baths, molds, doors creaking etc. If you procrastinated, and can't afford to follow step 0 (i or ii), get it done, keep a copy and send it in letter form to him/her anyway. State a fair time to get the deficits corrected - 2 weeks. (If you give 3 months, its obviously not a big issue for you)
Some contract states the responsibility of "minor reparation /Kleine instandhaltung" towards the rentee, over time, in which case say 6-8 months after contract signature, up to 100€ is deemed acceptable and leaking taps/ loose door handles will be for your own account.
There are rent reduction tables based on Legal proceedings.
a) For the inability to use the Kellerraum, WuM 1981, U19 allowed 10% rent reduction.
b) Leaking taps - not mention
c) Partly closing doors -not mentioned (Only Missing inner doors, Altona ZMR 2008, 298 allowed 25% rent reduction.
so you have roughly 10% deficit -give or take
A deficit is usually defined at 10% value of the rent (LG Münster). Only when reaching a 22% deficit you are allowed to exit the contract without notice. You have a marginal case for extreme measures. Avoid nitpicking minor issues but be firm on documenting the original state (before you moved in). This will be a major help when you are leaving and reparations are needed.
Consider a sample letter :
Mängelanzeige
Frankfurt, den 18 September
Sehr geehrter Herr Thickskinned,
in meiner Wohnung ist folgender Mangel/sind folgende Mängel aufgetreten:
........................................................
Gemäß § 535 BGB sind Sie zur Instandhaltung verpflichtet.
Ich bitte Sie, den Mangel/die Mängel innerhalb von zwei Wochen, spätestens bis zum ... beseitigen zu lassen.
Bis zur endgültigen Beseitigung des Mangels/der Mängel werde ich die Miete unter Vorbehalt zahlen. Dies betrifft auch schon die bereits für diesen Monat gezahlte Miete.
Mit freundlichen Grüßen
MYaqoob NiceGirl
* siehe hierzu unter „Mängelbeseitigung: zusätzliche Maßnahmen