How to replace an old toilet cistern with a new one

What you need

• 13 and 17 mm open-ended spanners or an adjustable spanner
• Large flat screwdriver
• Flat-nose pliers
• Sponge, bucket and rags
• Stanley knife and plastic scraper
• Small hacksaw in case the bolts are rusted
• New cistern of the same model as the pan with dual-flush mechanism included (Roca Victoria, Dama or Meridian, 60 to 120 € at Leroy Merlin or Bricodepot)
• Foam rubber cistern-to-pan doughnut seal, if not supplied with the cistern (4 to 8 €)
• Brass fixing bolt kit with conical rubber washers and metal washers (4 to 6 €)
• Stainless steel braided flexible hose 3/8 to 1/2 inch, 30 or 50 cm (3 to 6 €)
• New 1/2 by 3/8 isolation valve if the current one is stiff (5 to 8 €)
• Cleaning vinegar and WD-40 penetrating oil

Step by step

1. 1

   Turn off the water and empty the old cistern

   Close the isolation valve fully. If it will not close or leaks, shut off the mains stopcock for the flat. Flush, remove the lid and sponge out the bottom of the tank.

2. 2

   Disconnect the flexible hose

   With the bucket underneath, undo the hose nut at the cistern with the 17 mm spanner. If the hose shows rust or the outer rubber is cracked, do not reuse it.

3. 3

   Loosen the fixing bolts

   Under the back of the pan there are two wing nuts or hex nuts. Hold the bolt head from inside the tank with the screwdriver and loosen the nut from below. If they are rusted, spray WD-40, wait 10 minutes and, if they still will not move, cut the bolt with the hacksaw below the pan, protecting the ceramic with a rag.

4. 4

   Lift off the cistern and clean the pan

   Hold the tank with both hands and lift it straight up. Remove the old foam seal from the pan outlet and scrape off any residue with the plastic scraper. Clean the area with vinegar and dry thoroughly.

5. 5

   Prepare the new cistern

   Fit the flush valve if it is not pre-assembled (base with seal and large nut underneath, hand tight). Place the new doughnut seal over the flush valve nut on the outside of the cistern base. Pass the new bolts with their conical washers through from inside the tank.

6. 6

   Seat the cistern and tighten

   Lower the cistern onto the pan, lining the bolts up with the holes. Fit washer and nut from below, tighten by hand and then half a turn with the spanner on each side, alternating. Check the cistern is level and does not rock.

7. 7

   Connect the water and adjust

   Screw the new flexible hose onto the isolation valve and the cistern, no PTFE, hand tight plus a quarter turn with the spanner. Open slowly, let it fill, set the float so the water level sits 2 cm below the overflow, and adjust the push button height with the lid on.

8. 8

   Test and check for leaks

   Flush five or six times in a row. Run dry kitchen paper around the doughnut seal, the bolts and the hose. Check again after two hours and the next day: a badly seated seal takes a while to start dripping.

Before replacing the cistern: which model you need

A close-coupled cistern sits on the back of the pan and flushes through a central outlet sealed with a foam rubber doughnut seal. The distance between the two fixing bolts and the position of that outlet change from one model to the next. That is why a Roca Victoria cistern will not fit a Roca Dama pan, even though both are Roca. Look for the model name on the sticker inside the lid, stamped on the back of the pan, or on the invoice from the bathroom refit.

If the pan is a Roca Victoria, Dama or Meridian, a new cistern is still in the catalogue: 60 to 120 € with a dual-flush mechanism included, from Leroy Merlin, Bricodepot or any plumbers' merchant in Valencia and Alicante. If it is an old discontinued model (Roca Lucerna, Gala Marina, Sangrá, Bellavista, Jacob Delafon from the 70s and 80s), there is no guaranteed compatible cistern and the sensible move is to replace the whole toilet: a complete Roca Victoria with pan and cistern costs 120 to 180 € and fitting is 90 to 150 €.

If your cistern is high level (hung on the wall with a flush pipe) or concealed (Geberit, Roca In-Wall, with a push plate on the wall), this process does not apply. A high-level cistern is replaced with a new close-coupled toilet, and a concealed one is repaired through the push-plate opening.

• Measure the distance between the two fixing holes on the pan (on Roca it is usually 15 or 20 cm, but it varies).
• Check where the water enters: side or bottom, and that the new cistern has the inlet on the same side or comes blank for drilling.
• Always buy the cistern with the mechanism included: fitting one separately costs more and gives more adjustment problems.

Common mistakes when replacing a bathroom cistern

The most common mistake is reusing the old doughnut seal. That foam rubber has been squashed flat for 20 years and will not seal again; it drips behind the pan by the third day. A new seal costs 4 to 8 € and comes with many cistens. The same goes for the fixing bolts: if they are rusty, replace them with a brass kit with conical rubber washers.

The second is tightening the bolts until the cistern cannot move at all. Ceramic is not metal: tighten by hand, then half a turn alternating sides, and stop as soon as the cistern stops rocking. If it still leaks, the problem is a badly centred seal, not a lack of torque.

The third is forgetting to check the isolation valve. If it is 20 years old and does not shut off properly, change it now while the mains is already off; there is no better moment. And the fourth is putting PTFE tape or silicone on the flexible hose: the flat rubber washer seals on its own, and PTFE only helps the thread cross.

When to call a professional

Call us if the pan is a discontinued model and the whole toilet needs replacing, if the fixing bolts are rusted solid and will not come out (they need cutting with a grinder or hacksaw without touching the ceramic), if the isolation valve leaks, or if the outlet to the drain has a lead or fibre cement connector, which is common in older buildings in Valencia, Alicante or Alcoy.

Through our plumber service, replacing a toilet costs 90 to 150 € in labour, not including the toilet itself, and includes removing the old one and the final adjustment. If we only replace the cistern on a pan in good condition, the price sits between a mechanism replacement (60 to 110 €) and a full toilet swap, and we give you a fixed price on WhatsApp from a photo. We arrive in 20 to 45 minutes in Valencia, Alicante, Torrevieja and Benidorm. All rates are in how much a plumber charges. 6-month written guarantee and an invoice with IVA (VAT).

Tips for the coast: limescale, damp and second homes

With the hard water in Alicante and Valencia, the new cistern mechanism will last longer if you clean the fill valve filter once a year and do not use chlorine tablets inside the tank. Choose a cistern with a 3 and 6 litre dual flush: with water prices in the Valencian Community, a family saves 20 to 30 m³ a year compared with an old 9 or 12 litre cistern.

If the flat is a second home, close the isolation valve when you leave. And if the toilet has floor fixing bolts rusted by salt air (common on the seafront in Torrevieja, Santa Pola or Dénia), take the chance to swap them for stainless steel. Before replacing the whole cistern, check whether the fault can be fixed with a spare part: see toilet cistern keeps running, toilet cistern not filling and repairing a Roca cistern mechanism.