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For a Flushmate 503, match the check to the symptom: weak flushing calls for checks of the lever, water supply, inlet screen, bowl passages and pressure; a slow refill calls for supply and pressure checks; and a slow-draining bowl points to a blockage in the bowl, drain or vent. The 503 is a 1.6-gallon-per-flush pressure-assist system with a manufacturer-stated operating range of 20–80 psi. The steps below follow Flushmate/Sloan guidance and are checks, not a remote diagnosis.
How the Flushmate 503 works
A pressure-assist system uses water-supply pressure to power the flush. Flushmate explains that “All pressure-assist toilets get their energy from the water supply line.” Its product information lists the 503 at 1.6 gallons per flush and a minimum operating pressure of 20 psi; the manufacturer’s 2020 maintenance guide gives the 503 Series an operating range of 20–80 psi. Check the pressure requirement for your particular fixture and system rather than assuming every Flushmate model has identical specifications.
Before troubleshooting
- Find the shutoff valve supplying the toilet and check that it is fully open when the symptom-specific steps call for it.
- Do not treat a slow-draining bowl as a pressure-vessel refill problem. The two symptoms have different checks.
- If a check requires removing or adjusting a component and you are unsure how to do it safely, consult the official owner or maintenance guide or contact Flushmate support.
Flushmate 503 troubleshooting by symptom
Poor or weak flush
- Check the lever’s overall height in relation to the frame; adjust it if needed.
- Confirm the water-supply valve is fully open.
- Clear the supply line and clean the inlet screen.
- Check the bowl’s main jet, rim holes and trapway for blockage. Also check the drain line and vent.
- Verify supply pressure. The manufacturer’s stated operating range for the 503 Series is 20–80 psi.
If the flush remains weak after these checks, consult the official manual or contact support with the system model information.
Pressure vessel takes a long time to refill
- Make sure the water-supply valve is fully open.
- Clear the supply line and clean the inlet screen.
- Check the supply pressure against the manufacturer’s 20–80 psi operating range for the 503 Series.
Noisy refill
- Clear the supply line and clean the inlet screen.
- Flush the toilet, then hold the handle down for 30 to 40 seconds to flush the system, as the manufacturer’s maintenance guide instructs.
This is the published procedure, not a guarantee that noise will stop. If it persists, consult the official guide or support.
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- REPLACEMENT FLUSH VALVE CARTRIDGE: This replacement flush valve cartridge kit is designed by Sloan Flushmate for every Flushmate system. The Cartridge delivers regulated GPF for a consistent, high-performance flush. Built with corrosion-resistant materials and engineered for long-lasting durability, it ensures reliable performance and easy maintenance.
- OEM FLUSHMATE CARTRIDGE: This is an original equipment manufacturer (OEM) replacement cartridge, designed for use with 500, 501, 501A, 501B, 503, and 504 series Flushmate Tank systems assemblied in USA.
- COMPLETE KIT FOR EASY REPLACEMENT: The package contains the Flushmate brand valve cartridge, duckbill valve, and lower supply filter screen, providing everything needed for a full replacement and restoring flushing efficiency.
- FIX LEAKS & RESTORE PERFORMANCE: Replacing the Flushmate cartridge resolves common problems such as continuous water flow and leakage, bringing your toilet back to peak flushing performance.
- QUICK & EASY INSTALLATION: Installing the Flushmate cartridge is simple and can be done with basic tools or by using the Flushmate cartridge wrench (ST100500) or 3-in-1 wrench (ST100100). Regular replacement and maintenance ensure long-term performance and efficiency of your Flushmate system.
Water continues to flow through the vessel and it will not refill
- Check the lever height in relation to the frame and adjust if required.
- Check the cable connections to the frame and lever; adjust if needed.
- Confirm the supply valve is open and the supply line and inlet screen are clear.
- Check the cartridge and adjust it if required, following the manufacturer’s guidance.
Handle does not activate the flush
- Check the cable cassette connection and the cable connections to the handle, frame and lever; adjust if needed.
- Confirm the water-supply valve is fully open.
- Clear debris from the supply line and inlet screen.
Bowl water stays high or drains slowly
Check the bowl’s main jet, rim holes and trapway, along with the drain line and vent, for blockage. These are the manufacturer’s checks for slow drainage; they are separate from pressure-vessel refill troubleshooting.
Tank leak
- Check that the tank-to-bowl gasket is aligned properly.
- Inspect the tank bolts and washers.
- Replace a cracked tank. Do not overtighten tank nuts: the manufacturer warns that overtightening can crack the tank.
Avoid chlorine in-tank cleaners
Do not use in-tank cleaners or deodorizers containing chlorine (calcium hypochlorite). Flushmate warns that these products can seriously damage the Flushmate and tank fittings, leading to leakage and property damage.
Rank #2
- 【Replace】 The C-100500-K Replacement Flush Valve Cartridge Assembly is for Power Flush Toilet Replacement Part. The C-100500-K Flush Cartridge Kit Compatible with M-101526-F3, M-101526-F4 Pressure Assist Tank.
- 【Compatible】The Model C-100500-K Flush Valve Cartridge Assembly Compatible with 500, 501, 501A, 501B, 503 and 504 Series Tank Systems. I - 501/501A, II - 501B, III - 503, IV - 504 series of toilet.
- 【Upgraded】The Flush Cartridge Kit is made of durable ABS materials, cost-effective and good value for money, the Flush valve cartridge assembly is after strict quality inspection and testing before leaving factory, exceed OEM manufacturing requirements, package include Duckbill Valve, Filter Screen, Cartridge Assembly.
- 【Easy to install】 The C-100500-K Cartridge Kit is easy to install, no special tools are required, remove the old Flush Cartridge and replace new Flush Valve Cartridge Assembly C-100500. The Cartridge Parts is made of high quality material, heat resistance, wear resistance, more durable and have a longer service life. Please Wear work gloves to protect your hands before install.
- 【Excellent Flush Valve Cartridge】This C-100500 Replacement Cartridge Part.
Identify the exact system before ordering parts
Flushmate lists more than one 503 replacement configuration for different toilet tanks and original equipment manufacturers (OEMs). A generic “503 replacement” label does not establish that a unit fits your toilet.
- Locate the serial number on top of the Flushmate unit inside the toilet tank.
- Read the sequence between the dashes. Flushmate’s example is 010120-F31-1001; the center sequence, F31, identifies the system for parts lookup.
- Use Flushmate’s part finder to check the toilet and unit information before ordering. The manufacturer lists specific 503 replacements for combinations including Kohler K4404 and Gerber 28-385, as well as other OEM tanks.
For instance, do not assume M-101526-F31 is a universal 503 replacement. Confirm compatibility using the toilet OEM and serial sequence, then verify flow rate and minimum pressure against your fixture documentation.
Rank #3
- Precise Compatibility: Solve the trouble of mismatched toilet replacement parts, this flush valve cartridge kit matches OEM C-100500-Kit and perfectly fits Flushmate 500 501 503 504 series toilets, supporting quick and accurate replacement without extra modification
- Optimized Flushing Performance: Fix weak and incomplete flushing issues of old toilet valves, this toilet flush cartridge adopts upgraded water flow structure to stabilize flushing effect, realizing smooth flushing while cutting down unnecessary water consumption for daily use
- Durable Structural Design: Avoid frequent replacement of fragile toilet accessories, this toilet flush valve component features stable internal structure, maintains consistent working performance for a long time and reduces daily maintenance troubles
- Seamless Toilet Matching: Improve the inconsistent appearance of replaced toilet parts, this white flush valve cartridge comes with neat white finish, perfectly blending with most toilet appearances to keep integral and clean bathroom decoration style
- Premium Abrasion Resistance: Prevent part aging and damage caused by long-term water contact, this ABS flush valve cartridge is made of sturdy ABS material, resisting daily abrasion and adapting to different water quality environments for stable long-term use
Official manuals and support
Flushmate provides product, replacement-part and troubleshooting information through its official website. Its published support contact is 1-800-533-3460, Monday through Friday, 9 a.m.–5 p.m. Eastern; check the official contact page for current details before calling.
Quick Recap
Rank #4
- Replaces Part Numbers:The C-100500-K flush valve cartridge assembly kit serves as a premium replacement part for power flush toilets. This kit is compatible with Flushmate flush valves and fits seamlessly with M-101526-F3, M-101526-F4 pressure assist tanks
- Compatible Models:TheC-100500-Kit toilet flush valve cartridge replacement part compatible with 500 501 501A 501B 503 504 Series Tank Systems and I-501/501A,II - 501B,III - 503,IV-504 series of toilet
- Qualitative Materials:This C-100500-K C-100500-Kit flush valve cartridge assembly kit made from high‑quality ABS material.The kit includes a flush valve cartridge assembly kit,a new duckbill valve, a paperclip a screw
- Problem Solving:The power flush toilet piston cartridge assembly is the main valve that opens and closes to deliver the water to the toilet bowl.If your toilet leaks,runs constantly, has poor flushing power or loud screaming noises,replacing the old cartridge with this C-100500-K C-100500-Kit flush valve cartridge assembly kit restores strong, reliable flush performance quickly
- Easy to install: The C-100500-K flush valve cartridge kit is easy to install, remove the old Flush Cartridge and replace new C-100500-K flush valve cartridge assembly. To Prevent the Water Would not Shut off When Installed and Unable to Flush the Toilet With it Installed, Before installing the C-100500-K Flush Valve cartridge, please search for relevant installation videos on the YouTube website
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