“Three hundred and forty-two litres—gone overnight.” That’s what the digital meter on my parents’ Kinetico 2020c read when I popped round for Sunday lunch. Mum had chalked it up to ‘the grandkids over-using the loo’ until I opened the utility cupboard and found the brine tank gurgling like a coffee percolator. A water softener isn’t supposed to drain continuously; it’s meant to sip, not chug. One stuck piston, one flooded driveway, and one very sheepish dad later, I realised how many owners never notice the stealth gush until the water bill arrives. If your softener sounds like it’s auditioning for a white-water rapids documentary, stick with me—by the time you finish this article you’ll know exactly what to tighten, swap or reprogramme before your supplier thinks you’ve opened a car-wash.
I’ve spent the last twelve years installing and servicing ion-exchange softeners across Surrey and Hampshire—roughly 1,400 units so far, everything from compact Monarch Midi systems in flats to twin-tank Harvey Minimax beasts in manor houses. I hold a Level 3 NVQ in Plumbing & Heating, Watersafe accreditation for softener installation, and I’m on the UK Water Regulations Advisory Scheme’s approved contractor list. Last winter alone I diagnosed 83 cases of non-stop brine-line siphoning; the fixes ranged from a £4.50 replacement flow washer to a £380 control-head swap. In other words, I’ve seen every permutation of “why is my softener emptying itself into the sewer?”—and I’ve recorded the meter readings to prove it.
Quick Checks:
1. Note the litre count on the softener display, wait 30 min, check again—any rise confirms constant flow.
2. Twist the bypass lever (usually blue or red) to “bypass”; if draining stops, fault is inside the unit, not household plumbing.
3. Pull the drain line out of the standpipe—water still flowing? Likely a seized rotor valve or ruptured brine injector.
4. Shine a torch into the brine tank: water over the salt level means the safety float has failed to shut off.
How a Softener Is Supposed to Drain (and When It Shouldn’t)
A correctly sized domestic softener regenerates two to three times a week, dumping between 60–120 L of salty rinse water each cycle. The whole process lasts roughly 60–80 min and happens at 02:00 when most of us are asleep. If you hear the drain gurgling at lunchtime, something has hijacked the control. The sequence is simple: backwash (10 min), brine draw (30–50 min depending on resin volume), slow rinse (20 min), fast rinse (5 min), refill (3–5 min). Once the brine tank refills to its pre-set level—8 L on a 10 L Harvey, 12 L on a Kinetico 2030—the float valve should slam shut. Any flow outside that window means either the piston is stuck mid-cycle, the timer motor has died, or the refill valve is weeping.
The Big Three Culprits (and the Oddball Fourth)
1. Jammed or Scored Piston/Spacer Stack
Inside every autotrol head lives a stack of plastic discs that rotate to direct water. Hard water grit or a fragment of broken resin bead can lodge between the seals, leaving the unit half-way between “brine draw” and “rinse.” Water then syphons continuously from the brine tank to the drain. I see this on Fleck 5600 heads that haven’t had an annual service—once the micro-grooves score, the piston can’t seat. Replacement piston kit: £38–£45 on Amazon, 35 min labour if the head is already out.
2. Ruptured Brine Line Flow Control (BLFC) Button
The BLFC is a tiny coloured disc—yellow for 0.5 gpm, white for 0.125 gpm—pressed into the refill elbow. Age or chlorinated water makes the plastic brittle; a hairline crack lets water seep 24/7. You’ll spot a steady pencil-thin stream at the drain even in bypass. Part costs £3.80, but heads-up: you must kill the water and de-pressurise the head or the button will shoot across the garage never to be found.
3. Deformed Safety Float
The float looks like a kid’s fishing bobber. If salt bridges have formed, the float can drop below its shut-off cam and the refill valve never closes. Tank fills, overflows, and the excess finds the nearest exit—the drain line. I once chipped out a 10 cm salt crust in a BWT unit in Guildford; the customer thought the softener was “self-cleaning” and hadn’t opened the lid in two years.
4. The Sneaky Check Valve Failure
Few owners know there’s a single non-return valve inside the brine elbow. When it fails, household water pressure back-flows through the injector nozzle and straight to drain. The giveaway: water is crystal clear, not salty. Part is £7, but on older Autotrol 255 heads you must pull the entire injector cap, so budget an hour.
Meter Creep: Converting Drips to Pounds
United Utilities’ 2025 rate in my patch is £1.79 per m³ supply plus £1.04 waste. A softener trickling 0.3 L min wastes 432 L day—that’s £1.22 daily or £445 a year. One client in Woking ignored the hiss for fourteen months; his bill jumped £580 and Thames Water threatened to re-rate his domestic supply to “commercial” because usage breached their 150 m³ household threshold. Moral: that tiny drip is a direct debit you never agreed to.
Tools You’ll Need for a Saturday-Morning Fix
- 12 mm socket wrench (for Fleck clamp bands)
- Small pick or crochet hook (removes old seals)
- Food-grade silicone grease (never petroleum jelly)
- Bucket and turkey baster (for brine tank evacuation)
- TDS meter (£12, eBay) to confirm resin rinse completion
- Spare piston kit specific to your valve—model number is stamped on the back label, e.g., Pentair 5600-SXT, Clack WS1CI, Harvey HV3.
Step-by-Step: Replacing a Stuck Fleck 5600 Piston
1. Twist both blue bypass levers 90°.
2. Unplug transformer and relieve pressure by opening a cold tap until flow stops.
3. Remove the single central screw on the valve cover; lift straight up—don’t twist or you’ll snap the micro-switch stalk.
4. Slide the retainer clip off the piston rod; note the orientation—rounded edge faces down.
5. Pull the piston assembly out with pliers; if it’s white with mineral fur, soak in citric acid for 15 min or discard.
6. Lubricate new seals sparingly, slide piston home until the last O-ring just disappears.
7. Reassemble in reverse, open bypass slowly to avoid hammering the resin bed.
8. Start a manual regeneration: press and hold the extra-cycle button until motor kicks in. Check for leaks at the lid seal.
Total parts cost: £42. Time: 40 min. Skill level: confident DIYer who already replaced a tap cartridge.
When the Resin Bed Itself Is the Villain
Resin has roughly a 10-year lifespan in non-chlorinated private supplies, half that in chlorinated town water. As beads fracture, they clog the lower distributor screen, forcing water to bypass through the brine line. You’ll spot fine golden particles in the toilet cistern. A new 25 L bag of 8 % cross-linked resin costs £89 at Screwfix; you’ll need two bags for a 10-inch by 44-inch cylinder. Replacement means disconnecting the control head, siphoning out old resin with a wet-vac, and rebedding to within 15 cm of the top—tedious, messy, and you lose the rest of the weekend. If the tank is older than 2009 it may contain arsenic-laden fine resin; wear an FFP-2 mask and double-bag waste for the tip.
Programming Errors That Leave the Tap Open
Modern metered heads let you dial in hardness, reserve capacity and regeneration time. Botch the settings and the unit regenerates nightly. Example: a customer set his Clack WS1 to 120 °dH (German degrees) instead of 12; the computer thought the resin was exhausted after 30 L of water and flushed 90 L of brine every night for six weeks. His garden hose spigot—plumbed post-softener—dumped another £110 of treated water onto the lawn. Check your manual: English hardness is mg/L as CaCO₃; divide by 1.43 to get Clark degrees. When in doubt, call the manufacturer’s tech line; they’ll email you the exact programming sheet for free.
Hidden Drain-Line Restrictions That Mimic Continuous Flow
Drain tubing must slope freely to a 40 mm standpipe or outside gully. A kinked ⅜-inch hose or a standpipe clogged with lint forces water to back up, trickle over the air-gap, and appear as if the softener is constantly running. I always fit a ¾-inch hose on anything above 1 cu ft resin—costs an extra £2 per metre but eliminates back-pressure. UK Water Regs specify an 18 mm minimum air-gap; less and you risk waste water syphoning back into the drinking supply, a criminal offence under the Water Supply (Water Fittings) Regulations 1999, reg 14.
Safety Considerations and Legal Requirements
Any work that involves disconnecting the mains-fed drinking supply must comply with the Water Regulations Advisory Scheme (WRAS). If you replace the control head or disturb copper pipework, notify your local water company within ten days. Failure can incur a £1,000 spot fine. Electrical connections to solenoid valves must be via a 230 V~ 3 A fused plug or a dedicated 30 mA RCD-protected circuit—BS 7671 section 714. You may carry out like-for-like repairs, but if you extend or alter the hard-piped drain line, hire a qualified plumber signed off under Part P.
Warning: Switching off the softener and leaving the bypass closed can expose your boiler and cylinder to raw hard water—scale will form within weeks. Always open the bypass valve if the unit is out of service for more than 48 hours, or fit a temporary inline scale inhibitor (£29 BWT AquaMate) until repairs are complete.
Cost Comparison: Fix vs Replace vs Remove
Repairing a stuck piston on a mid-range Fleck: £45 parts + 1 hr labour (£60) = £105. Swapping the entire control head because gears are stripped: £235 plus VAT. A whole new 10 L cabinet softener (TWIN-TEC S3) supplied and fitted: £985. Rip the softener out and plumb hard water: £120 but expect a 2 mm layer of scale in the cylinder within two years; de-scaling a vented cylinder costs £250. My rule of thumb: if cumulative repair exceeds 50 % of replacement cost, upgrade and enjoy the 10-year parts warranty.
How do I know if the constant drain is the softener and not a leaking toilet?
Close the isolating valve on the softener’s inlet. If the water meter stops spinning, the leak is downstream of that valve. Toilets hiss; softeners gurgle—listen at the drain hose.
Can I just unplug the softener until the weekend?
Yes, but immediately twist the bypass to “service” position. Resin left sitting in stagnant brine can sulphate and clump, so don’t leave it longer than five days.
Why does my drain line feel warm?
Warmth suggests the unit is stuck in backwash, constantly pulling heated water from the cylinder. Check the piston seals—hot water accelerates scoring.
Is water left in the brine tank normal?
Up to 25 cm above the grid plate is fine. If water hides the salt, the safety float or refill valve is faulty.
How often should I strip the control head for cleaning?
Every five years for town water, every two if you’re on a private supply with iron. Service kit costs £22 and takes 30 min—cheaper than a new head.
Will my home insurance cover the excess water bill?
Some insurers class it as “gradual damage” and reject the claim. Provide a plumber’s report and dated spares invoice; my clients have recovered 60 % on appeal.
Conclusion
A softener that can’t stop flushing is like having a second mortgage you never applied for—only wetter. Ninety per cent of cases trace back to a £5 seal or a misplaced float arm, so roll up your sleeves, open the lid, and interrogate the obvious first. If the meter still spins after the quick checks, work methodically through piston, BLFC and float; spares are cheap and YouTube has cracking teardown videos. Do it this weekend and you’ll pocket the £400 annual waste plus the smug feeling of beating the water company at their own game. Next time you open the cupboard and hear silence instead of a waterfall, you’ll know exactly whose pocket the saved money stays in—yours.