Why is my dishwasher tablet not dissolving?
An undissolved tablet means the dispenser never opened, the water never got hot enough, or the spray never reached it — and the dispenser flap is by far the most common of the three.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 3 min
Short answer
Check nothing is leaning against the dispenser flap. It springs open partway through the cycle, and a tall plate, a chopping board or a baking tray in front of it holds it shut. If the flap opened and the tablet is still sitting there whole, the machine is not getting hot or the spray is not reaching it.
The dispenser is a spring-loaded flap that fires open at a set point in the cycle, usually after the pre-wash has drained. The tablet then drops into water that is being sprayed around the tub. Three things can break that chain, and the symptom tells you which: a tablet still in a closed compartment, a tablet sitting whole in the compartment with the flap open, or a tablet half dissolved and stuck in the bottom of the machine.
Step by step
- Look at the dispenser flap before you unload anything.Closed with the tablet inside means it never opened. Open with the tablet still in it means it opened and nothing washed the tablet out. That single observation splits the problem in two.
- Check what was leaning on the flap.The flap opens outwards into the lower basket area. A dinner plate, a chopping board on its side, a large lid or the corner of a baking tray in front of it will hold it shut against its spring. Reload with a clear space in front of the dispenser.
- Check the dispenser is clean and dry when you load it.Old detergent caked around the flap edges glues it shut. Wipe it out with a dry cloth and clear the corners with a toothbrush. Loading a tablet into a wet dispenser starts it dissolving early, which also gums the flap.
- Check the tablets themselves.Tablets absorb moisture from the air and go hard and chalky. Ones stored in a damp cupboard or with the bag left open dissolve badly. Keep them sealed and dry, and do not unwrap them — modern wrappers are meant to dissolve.
- Check the middle spray arm is turning.On most machines the water that washes the tablet out of an opened dispenser comes from the arm under the upper basket. If a tall item is blocking that arm, the tablet sits in an open compartment untouched. Spin both arms by hand before every cycle.
- Check the machine is heating.Tablets are formulated to dissolve at wash temperature. If the load comes out cold and there is undissolved detergent, the heater is the problem, not the dispenser. That is an engineer's diagnosis.
- Do not put the tablet in the bottom of the machine as a workaround.It is a widely repeated tip and it is a poor one: the tablet dissolves during the pre-wash and gets drained away before the main wash, so the load gets almost no detergent. Fix the dispenser instead.
- Try a powder or gel if the machine will not cooperate.On a machine with a weak dispenser spring or a very short cycle, powder dosed into the dispenser dissolves more readily than a compressed tablet. It is also the only way to dose smaller amounts for small loads.
Common mistakes
- Unwrapping the tablet first — Modern wrappers are water-soluble film designed to dissolve in the wash. Unwrapping exposes the tablet to moisture in the dispenser and makes it more likely to stick, not less.
If it doesn't work
Chalky white residue on everything and part of a tablet in the sump
Cause: Tablet released but never fully dissolved and was redeposited — Fix: Run a hot empty cycle to clear the machine, then fix the underlying cause — usually the middle spray arm or a cycle too cool for the tablet.
Flap opens but the tablet is welded to the compartment
Cause: Damp got into the compartment before the cycle started — Fix: Dry the compartment before loading, and stop loading the machine hours before you run it with the tablet already in.
Happens only on the quick programme
Cause: The programme is too short and too cool for a compressed tablet — Fix: Use powder or gel on short programmes, or use a programme with a proper main wash.
Questions people ask
Is it worth using two tablets for a very dirty load?
No. The dispenser only opens once, so the second tablet dissolves during the pre-wash and is drained away. Use the intensive programme instead, which changes the water more times and runs hotter.