Submersible Pump Float Stuck or Won’t Drain Low? What to Check

The cellar is filling and the pump won’t kick in, or it stops with a puddle still on the floor. Usually the float is snagged, the inlet can’t reach that low, or the pump doesn’t suit what’s in the water. Here is how to tell which.

At PartsForMachines we list 112 products in Submersible Water Pumps from T-T Pumps, Draper and Sealey. They range from clean and dirty water pumps to low-level puddle pumps and float switches.

Why Won’t My Pump’s Float Switch Start or Stop the Pump?

Usually because the float can’t move. It has to rise with the water to switch the pump on, then drop to switch it off. A float caught on the pit wall, the pump body, a pipe or debris leaves the pump sitting idle or running on.

Clear the pit so the float swings freely. Then, with the pump standing in water, lift the float by hand: if the motor starts, the switch and motor work, so look for whatever is stopping the float rising. On the WPD235P dirty water pump, a bracket fixed on the cable lets you set the cut-out at several heights.

How Low Will a Submersible Pump Drain a Flooded Cellar?

Only as low as its inlet and cut-out allow, so check the minimum water depth before you buy. A dirty water pump such as the WPD235A works down to 40mm, which leaves a shallow layer across a level floor.

For the last of it, sweep the water towards a 2mm low-level pump such as the WPL117A. It is designed for clean water, takes particles up to 5mm and has an automatic cut-out. On a big job, run the dirty water pump first and finish with the low-level one.

Silt, Stones or Clean Water: What Solids Size Stops a Pump Clogging?

The pump’s maximum particle size, sometimes called free passage, must cover the largest solids in the water. Clean water pumps take only small particles, for example 0.5mm on the WPS92A and 5mm on the WPL117A, so leaves and gravel can block them. Dirty water pumps such as the WPD235P pass solids up to 30mm.

Gritty site water calls for a pump built for it. A sand-and-gravel vortex pump such as the PH/LIBV750/230V has 38mm free passage, and its maker rates it highly resistant to sandy, gravelly water. Whatever you use, stand the pump on firm ground, or on a brick where the bottom is muddy.

Can a Submersible Pump Run Dry, and What Stops It Burning Out?

Try not to let it: running dry increases wear, so the aim is to stop the pump before the water runs out. A float switch or automatic cut-out does that as the level falls. A float-switch pump such as the 98918 cuts its motor when the water drops, and thermal overload protection guards it against overheating.

Manual pumps, such as the PH/T400/230V drainage pump, have no float, so they keep running for as long as they are powered. With one of those, stay close by and switch it off as the water runs out.

What Should I Check Before I Buy?

• the water: clean, dirty or sandy, and the largest solids the pump must pass
• the minimum water depth, which tells you how low it will drain
• float switch or manual control, and whether the cut-out height can be set
• the height from the water to where the hose empties, against the pump’s head figures
• the supply: 230V, 110V site power or 400V three-phase, and the cable length to the socket

Browse the Submersible Water Pumps range, or contact the PartsForMachines team by WhatsApp, telephone or email with the depth of water, the height you need to lift it and what is in it.

Product options, delivery options and returns terms are shown on each product page. A 30-day return policy applies to eligible items.

Frequently Asked Questions

How much head do I need to empty a cellar?

More than the height from the water to where the hose empties. Check the rated figure, not just the maximum: the PH/T400/230VF reaches 12m maximum head, but moves 110 litres a minute at 8m against 220 at best, so flow falls as lift rises.

The pump runs but nothing comes out of the hose. Why?

Check the outlet hose first, as a kink can stop the flow completely. Then lift the pump out and make sure the inlet isn’t blocked with silt, leaves or other debris.

Could my pump be air-locked?

It can happen: air trapped in the pump can stop it moving water. Some pumps let the air out through an automatic vent or air relief valve; the Goliath Super sump pumps, for example, have one built in.

Why won’t my pump start in a shallow puddle?

Some pumps need noticeably deeper water to start pumping than they leave behind when they stop. Check the minimum water depth before you buy, stand the pump at the deepest point, or finish with a low-level pump that works in just a few millimetres.

Does a cellar or site pump need RCD protection?

Yes, run it through an RCD. Pump makers recommend one for pumps used in water, and one specifies a 30mA trip. On building sites, a 110V pump such as the 98920 is suitable for use with standard site transformers.

Where should a high-water alarm float sit?

Above the level where the pump switches on, so it only sounds if the pump fails or can’t keep up. A clean-water change-over float switch such as the LT/FLO107-10M can operate a pump or trigger a high or low-level alarm.

Do I need a sump pit in the cellar floor?

Not always, but a pit gathers the water in one place and gives the float room to move. Some sump pumps state a minimum pit size: the Goliath Super needs at least 250mm x 250mm.

Can I use a clean water pump in a pond or ditch?

Only if the water is fairly clear. Clean water pumps pass only small particles, so leaves, silt and grit can block the inlet. For pond or ditch water, a dirty water pump with a larger free passage is the safer choice.

Can I leave a float-switch pump to run on its own?

Yes, that is what the float is for. Check it every so often: clear debris from around the float and the inlet, and make sure nothing has drifted against the float that could hold it up or down.