How to Tell Why Your Toilet Tank is Not Filling — and How to Fix It

There are various household problems that require immediate attention. For many of us, the toilet tank not filling quickly enough is one that we tend to put off. Sure, its annoying and can be inconvenient, but it’s not something urgent like a crack in the toilet bowl! Who wants to spend money on a plumber when there are more important things for your budget to go towards? Yet, the truth is it’s a relatively simple fix. It requires just a few additional parts, perhaps a couple of tools that you probably already have to hand, and about thirty minutes of your time. Even if you’re not renowned in your neighborhood for being the most handy around the house, you’re still likely to be able to take this job on and succeed.

Let’s take a look at a few of the likely reasons why your toilet tank is not filling, and the solutions that get your toilet running correctly again.

image of bathroom to demonstrate a toilet tank not filling

Why is Your Toilet Tank Not Filling?

If your cistern is taking it’s time to fill, or not filling at all, there are handful of possible reasons for this. Identifying the cause is your first step to finding the right solution.

1. The float ball is at the wrong height

This is one of the most common reasons that older models of toilet tank are not filling. The float ball is in place to regulate the amount of water that re-enters the tank after you flush. It’s a smart and simple solution that causes the float arm to automatically block the water inlet, but it also relies on being set to the right position in order to let the right amount of water back into the tank after each flush. If you’re finding that each press on the handle only releases a small volume into the bowl, leaving you unable to clear away waste — this is probably the culprit.

A plastic float ball may be the problem with a toilet tank not filling

In order to confirm the cause and solve the issue:

  • Remove the cistern lid.
  • Check to see if the water volume is low in the tank, but the float is still sitting on top of the water.
  • Firmly grasp the metal arm attached to the float ball, and bend the arm slightly upwards.
  • Replace the ball in the tank.
  • This should make the ball sit higher in the water, allowing the tank to fill up correctly.
  • Keep adjusting as required.

2. There is debris in the fill valve

If your float ball is in the correct position, but not enough water is entering the tank, chances are there’s debris preventing water from entering. There is no reason that the items you flush should be preventing the valve from operating correctly. Rather, it’s more likely that foreign objects have washed up through the inlet. This means it’s time to get on some gloves and rummage around a little bit.

In order to confirm the cause and solve the issue:

  • Remove the cistern lid.
  • Turn off water inlet supply.
  • Identify the fill valve. This is the tube that usually sits on the left hand side, and connects to the water inlet system.
  • Remove the valve cap. This is usually done by pressing down on the cap and rotating counter-clockwise.
  • Remove any obvious debris in the tube.
  • Cover the top of the valve tube with an inverted plastic cup.
  • Flush the toilet to remove any smaller debris.
  • Reassemble the valve.

3. The fill valve is incorrectly set

Many newer toilets don’t have an external float ball. As a result, the water is regulated by setting the fill valve itself at the correct height and flow level. In order for the fill valve to let in the right amount of water, it needs to be adjusted to a position in which it only shuts off the water flow when it reaches the water line mark of the cistern. A toilet tank not filling as a result of this issue usually means that the valve is set too low in the water.

In order to confirm this is the case and solve the issue:

  • Remove the cistern lid.
  • Check to see whether the water meets the water line mark. This is stamped on the inside of every toilet tank.
  • Identify the adjusting screw on the top of the fill valve, this is usually attached to a plastic arm
  • Flush the toilet to remove remaining water from the tank, and relieve pressure from the fill valve.
  • As the water begins refilling after the flush, use a screwdriver to turn the adjusting screw clockwise.
  • Once the valve has ceased refilling, check to see whether the water hits just below the water line mark.
  • If the water is below the mark, repeat the process. If it is above the mark, repeat the process, but turn the screw counter clockwise.

4. The fill valve is damaged

Often, the first sign that there is damage inside the toilet cistern tank is excessive noise. There could be a range of reasons why the toilet is noisy, but if it is hissing, it is likely to be that the fill valve is damaged. This is often coupled with the tank either taking a long time to refill, to the extent that the next time someone flushes there isn’t enough water to clear away the waste. There’s no need to panic in this scenario, and calling out a plumber shouldn’t be necessary. you won’t be able to repair a damaged fill valve, but it’s a relatively simple replacement.

Image of a fill valve for fixing a toilet tank not filling

In order to confirm this is the case and solve the issue:

  • Remove the cistern lid.
  • Confirm that the top of the fill valve is leaking, and that the tank is filling in a slow trickle.
  • Obtain a replacement fill valve.
  • Turn off the water inlet supply.
  • Flush out any remaining water in the tank.
  • Fill valves are usually attached to the base of the tank by a clip. Push the clip up, and pull the old fill valve off the base stem, and out of the tank.
  • Push the new fill valve down onto the base stem, and secure it with the clip.
  • Turn the water back on and adjust as required (see above).

5. The water pressure is too low

If you’ve attempted to troubleshoot all the possible issues inside a toilet tank that’s not filling, then it might be the case that the problem is not with the toilet at all. Low water pressure in the pipes leading to your toilet tank can also cause your water level to remain low, or fill slowly. This can be due to rusted or leaking pipework either on your property or leading up to your house. Owners of old homes often find that low pressure can be an issue.

Unfortunately, this is one of the few occasions that a qualified plumber is a necessary expense. We’re not talking about a simple case of unclogging your toilet that you can achieve without even having a plunger! It’s not advisable to attempt these repairs and replacements yourself unless you have the requisite experience. If you’ve ruled out all other causes of a toilet tank not filling, it’s time to call in the professionals.

Fixing the Fill

Undertaking any kind of plumbing issue in your home can be a daunting task. That said, most issues inside the cistern are relatively easy to solve. With a little confidence, and some know-how, you can keep your toilet running in peak condition. That said, it’s worth conducting some regular maintenance, such as performing yearly check ups on the floats, valves, and gaskets to make sure there isn’t any deterioration that could cause problems in the future. Once every few years, it’s also advisable to install a full toilet repair kit, even if there aren’t any pressing issues.

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