While we enjoyed our stay at the Central House, I would like to mention a few things to be wary of prior to booking your stay.
About the check-in: The keycard that we were given on Day 1 did not work and we had to head back to the reception to get the key reactivated.
About the room: Note that if you are booking a double room for 2 guests and expecting to have 1 double bed + 1 bunk (as shown on the pictures), you will be asked to pay extra money upon arrival in order to get the bunk bed open. (20euro extra per night) - a bit surprising when none of this is mentioned on the listing. There are not duvets in the room as the only beddings provided are sheets. The Air Con does work however you cannot set it higher than 20.5 degrees which makes the room either really cold or really warm (if you decide to turn it off).
About the pool: Don't expect one! While the pool was one of the main reason why we booked the Central House, we were shocked when we saw that there was simply no water in the pool and that after mentioning it to the reception we were told that 'the maintenance guy didnt come' and that it wasn't exactly a pool anyway but a 'charco' (puddle). Slightly disappointing when visiting Madrid in July under a 43 degrees heat.
About the Hostel in general: The commons are really lovely and clean however note that the vending machine was out of order for one day making it impossible to get drinking water in the hostel.
Overall I would recommend booking the Central House if you are only looking for a great central location and a quiet environment. Don't expect luxury or a rooftop pool.