A Hot Machine In Hard Water Will Scale Up. The Only Question Is How Fast

The heating coil is the most expensive part of a hot water machine. It is also the part you never see.

It sits inside the machine as a long steel tube wrapped in a spiral. Water goes in cold and comes out hot. Nothing about it looks like a wearing part, so nobody treats it as one.

Then one day the machine takes twice as long to reach temperature. It burns more fuel getting there, and pressure at the lance has dropped.

By then the coil has been closing up for two years.

What scale actually is

Hard water carries dissolved calcium and magnesium. In most of the South East that means a lot of it, because the water comes through chalk.

Here is the part that matters. Those minerals become less soluble as water gets hotter, not more.

Heat the water, and they drop out of solution, and they stick to whatever surface is hottest.

In your machine, the hottest surface is the inside of the coil. So the scale forms where you least want it: the smallest bore, on the most expensive component.

A cold water machine gets some scale in the pump and the valves. A hot water machine gets it on the coil, and it gets it far faster.

Why this part of the country is the worst case

Water hardness varies a great deal across the UK. The west and north are mostly soft. The South East and East Anglia are mostly hard to very hard.

We are in Leighton Buzzard. Almost every machine we service runs on hard water, and we see the results on the bench every week.

That is not a reason to avoid a hot machine. It is a reason to treat descaling as routine maintenance rather than a repair.

An operator in Cumbria might get away with ignoring it. Here you will not.

What it costs you before it kills anything

Scale does not announce itself, and it taxes you quietly for years first.

Fuel. Scale is an insulator. A coated coil transfers heat badly, so the burner runs longer to reach the same temperature. On a machine working daily, that is a real number by the end of the year.

Output. The bore closes up, so flow drops. Less water through the lance means slower cleaning, and slower cleaning means longer on every job.

Pressure. Restriction upstream of the nozzle shows up as reduced pressure at the surface. Operators usually blame the pump.

The coil itself. This is the one that ends machines.

A heavily scaled coil develops hot spots where the metal cannot shed heat into the water. Steel that runs too hot fails in the end, and a coil replacement is a serious bill.

How to spot it before the bench does

Five signs, and the first two show up long before the others.

It takes longer to reach temperature. You know your machine's normal warm-up. When that stretches, suspect the coil.

The burner cycles more often. It is working harder to hold the same output temperature.

Fuel use creeps up without the workload changing.

Flow at the lance drops, and a new nozzle does not fix it.

The machine runs hot around the coil housing because heat is not going into the water.

Any two of those together mean book it in. Waiting costs more than descaling does.

Descaling, and how often

Descaling circulates an acidic solution through the coil, which dissolves the deposit and flushes it out. That is a chemical job, not a mechanical one, and it needs doing right.

Three things drive the interval. How hard your water is, how many hours the machine runs, and how hot you run it. Hotter and busier means more often.

As a working rule in this region, a hot machine in daily commercial use wants descaling annually. It forms part of a full service.

A machine on lighter duty can often stretch longer. A machine running near maximum temperature all day may want it sooner.

We descale both ways. Bring it to the workshop, or let our mobile engineers do it on site. On-site suits anything plumbed in, wall-mounted or otherwise fixed.

One warning on doing it yourself. Descaling chemicals are strong acids, and the coil is a pressure component.

Get the concentration or the dwell wrong, and you attack the metal rather than the deposit. Use a product made for the job, such as an acidic scale and deposit remover. Follow the dilution on the label.

Never mix it with anything alkaline. That includes the traffic film remover sitting next to it in the store.

Slowing it down

You cannot stop scale in hard water, but you can change how often you pay for it.

Filter the inlet. A filter does not remove dissolved hardness, so it will not stop scale.

It does stop grit and rust from reaching the pump and the valves, which is a separate and cheap win. Our filtration guide covers what does what.

Soften the feed where it is practical. In a wash bay, a softener on the supply is the one thing that slows coil scaling. On a mobile machine, it is rarely workable.

Do not run hotter than the job needs. Every extra degree speeds up deposition. Most vehicle work does not need the maximum the machine offers, and 60 rather than 80 buys you coil life.

Flush after chemical use so nothing sits in the system overnight.

Keep the service record. Scale is gradual, so a written history tells you whether the interval suits your water and your hours.

Cold water machines are not immune

The coil is the dramatic failure, so it gets the attention. Cold machines scale too.

It collects in the pump head, on valve seats and around the unloader. The symptoms are familiar: pressure that will not hold, a valve that weeps, a machine that pulses.

That is slower and cheaper to deal with, but it is the same chemistry.

Are you on hard water with a cold machine that has never been apart? Worth raising at its next service.

Frequently asked questions

How often should a hot water pressure washer be descaled?

In a hard water area, annually for a machine in daily commercial use. It normally forms part of a full service.

Lighter use can stretch further, and machines run hot all day may need it sooner. Water hardness, running hours and operating temperature all drive the interval.

What are the signs of limescale in a pressure washer?

The earliest signs are longer warm-up times and a burner that cycles more often.

After that, fuel use creeps up and flow drops at the lance. Pressure falls, and a new nozzle does not restore it. The machine may also feel hotter than usual around the coil housing.

Can I descale a pressure washer myself?

You can, using a product made for the job and following the dilution on the label. Be careful.

Descalers are strong acids, and the coil is a pressure component. The wrong concentration or dwell time attacks the metal. Never mix a descaler with alkaline chemicals such as traffic film remover.

Does limescale damage cold water pressure washers too?

Yes, though more slowly. Without a heating coil, the scale collects in the pump head, on valve seats and around the unloader.

It shows up as pressure that will not hold, weeping valves or a pulsing machine. A normal pump service deals with it.

Will a water filter stop limescale?

No. A filter removes grit, rust and particles, not dissolved calcium and magnesium.

Fitting one is still worth doing, because it protects the pump and valves from mechanical wear. Only a softener on the supply reduces scale, and that normally suits static installations rather than mobile machines.

The bottom line

Every hot water machine on hard water is scaling up right now. That is chemistry, not neglect.

What you control is the interval. Descale on a schedule and the coil lasts the life of the machine.

Wait for the symptoms, and you pay in fuel and output for years, then pay again for the coil.

Watch the warm-up time, because it is the first thing to change and the easiest to notice.

RealKleen has serviced hot water machines on South East water since 1980. We do it in our Leighton Buzzard workshop and on site across the region. Tell us the machine, your hours and your postcode, and we will tell you what interval your water needs.