Drain & Sewer Emergency
Toilet Problems? Here's What's Actually Going On.
A toilet that won't flush or won't stop running are two different problems with different fixes. This guide covers both — and tells you when it's time to call a plumber.
What's Going On
Understanding the Problem
Toilets fail in two main ways: they won't drain (clogged or blocked), or the tank mechanism malfunctions and the toilet runs constantly or won't refill. A clogged toilet is a drain problem. A running toilet is a hardware problem inside the tank. The distinction matters because the solutions are completely different. A third, more serious scenario — the toilet is gurgling, slow, or backing up along with other drains — is a sign of a main sewer line issue, not a toilet problem at all.
Diagnosis
Common Causes
1Clog in the toilet trap
The toilet has a built-in trap — a curved section of porcelain — that holds water to block sewer gas. This is the most common spot for blockages. Excess toilet paper, wet wipes, or a foreign object gets stuck in the curve. The toilet may flush sluggishly or not at all, and the bowl may fill with water rather than draining. This is usually fixable with a flange plunger.
2Worn or warped flapper valve
The flapper is the rubber seal at the bottom of the tank that lifts when you flush and seals the tank when it refills. Over time, the rubber warps, hardens, or develops mineral buildup from Houston's hard water, and it no longer seals properly. The result is water continuously trickling from the tank into the bowl — that's the sound of a constantly running toilet. A replacement flapper costs a few dollars and takes about 10 minutes to swap out.
3Float set too high or faulty fill valve
The float tells the fill valve when to stop adding water to the tank. If the float is adjusted too high or the fill valve is worn, the tank overfills and water continuously drains into the overflow tube. You can usually see this by lifting the tank lid — if water is flowing into the vertical overflow tube, the float height needs adjustment or the fill valve needs replacement.
4Partial blockage in the drain line below the toilet
A blockage further down the drain line — past the toilet itself — can cause the toilet to flush slowly and the bowl to drain sluggishly even after plunging clears the trap. If plunging doesn't help after a few attempts, the blockage is deeper and requires a drain snake.
5Blocked or venting issue
If you hear gurgling from the toilet when you run a sink nearby, or the toilet gurgles after flushing, the vent stack may be partially blocked. The toilet needs air to drain properly, and without adequate venting, it creates a siphon effect that pulls water from P-traps and causes slow, noisy drainage.
6Cracked toilet flange
The toilet flange is the fitting that connects the toilet base to the drain pipe in the floor. In Houston slab homes, slab movement and soil expansion can crack or shift the flange over time. A damaged flange can cause the toilet to rock, leak at the base, or flush poorly. You may notice water or a dark stain around the base of the toilet after flushing.
DIY Troubleshooting
What You Can Try
Use a flange plunger (not a cup plunger) for a clogged toilet
A flange plunger — the one with a rubber extension that folds out from the cup — is designed specifically for toilets. Place it in the bowl to cover the drain opening fully, ensure you have a good seal, then push and pull with firm strokes. Don't plunge aggressively — slow, deliberate strokes that build pressure and vacuum are more effective. After 15–20 plunges, test with a slow flush.
Turn off the water supply if the toilet is overflowing
The water supply shutoff valve is located at the base of the toilet, behind and to the left or right. Turn it clockwise to shut off water flow to the tank. This prevents overflow while you work on the clog. If the bowl is already at the rim, do not flush again — it will overflow.
Check the flapper for a running toilet
Lift the tank lid and look at the flapper — the rubber disc at the bottom center of the tank. Press down on it with your finger. If the running sound stops, your flapper isn't sealing properly and needs to be replaced. Flappers are universal-fit at most hardware stores. Shut off the water supply, flush to drain the tank, unhook the old flapper, hook on the new one, and turn the water back on.
Check the float height for a constantly running toilet
With the tank lid off, look at whether water is flowing into the overflow tube (the tall vertical tube in the center of the tank). If it is, the water level is too high. Most modern fill valves have an adjustment screw or clip on the fill valve itself — turn or slide it to lower the water level until it sits about an inch below the top of the overflow tube.
Pour a bucket of water directly into the bowl to test if it drains
If you're not sure whether you have a clog or a flushing mechanism problem, pour a full bucket of water rapidly into the toilet bowl. If the water drains normally, the problem is in the tank (flushing mechanism), not in the drain. If it backs up, you have a clog.
Know When to Call
When to Call a Pro
Call ARG Plumbing at (832) 419-3411 if your toilet won't clear after a few attempts with a flange plunger, if multiple toilets are slow or backing up, or if you see water around the base of the toilet after flushing — that indicates a bad wax seal or cracked flange that needs professional repair. A running toilet can waste 200 gallons a day; if you can't identify or fix the tank issue yourself, it's worth a quick service call.
Pro Tip
Keep a flange plunger under every toilet in your home, not a cup plunger. Cup plungers are for flat drains like sinks and tubs. Using a cup plunger on a toilet barely creates any seal over the drain. The flange plunger's rubber extension fits directly into the toilet drain opening for real suction. It's a $10 tool that saves a lot of midnight panic.
Hristo
Master Plumber · ARG Plumbing