Gledhill StainlessLite Cylinders

What is a Gledhill StainlessLite cylinder

StainlessLite is Gledhill’s family of unvented, mains pressure, stainless steel hot water cylinders. Unvented means the cylinder is sealed and fed directly from the incoming cold main, so there is no cold water storage tank in the loft and the hot taps run at roughly the same pressure as the cold ones. That is why the range replaced so many vented copper cylinders through the refurbishment years.

Gledhill makes more than this one range, which is where confusion starts. The same badge appears on thermal stores, on the Pulsacoil family found in electrically heated flats, and on vented cylinders that are not unvented appliances at all. Those are different products with different controls and different parts, so the first job is to settle what you actually have. A StainlessLite is a tall insulated cylinder fed from the mains, with a control group on the cold feed, a separate expansion vessel nearby, and a discharge pipe to a tundish. If none of that is present, this page will not apply.

• Unvented: sealed, fed from the cold main, no loft tank, mains pressure at the hot taps.
• Indirect versions are heated by a boiler coil. Direct versions by immersion elements alone.
• A separate expansion vessel and a visible tundish are the signs that it is unvented.

Which StainlessLite do I have and which generation is it

Read the data badge on the casing. It carries the model designation, the capacity in litres and a serial number, and it is the only identification anybody should work from. Photograph it before you ring a plumber or a parts counter, because the exact designation is the first question you will be asked and a description of the cupboard is no substitute for it.

Generation matters more here than owners expect. The range has moved through an original StainlessLite, a StainlessLite Plus and the current StainlessLite Pro, and although they do the same job they are not the same appliance in service terms. The inlet control arrangement changed, the immersion and thermostat pocket details changed, and the spares list moved with them. An engineer who quotes a part before reading the badge is guessing, and guessing here means a second visit.

If the badge has been painted over or has fallen off, there are still useful signals. Look at the cold feed for a separate expansion vessel on a bracket, since StainlessLite uses an external vessel rather than handling expansion inside the cylinder. Look at whether the inlet controls are a run of individual brass fittings or a single moulded assembly. Note the shape, because slimline and horizontal variants exist and they narrow the list quickly.

Photograph two things before you call anybody: the data badge, and the pipework at the cold feed including the expansion vessel and the inlet controls. Those pictures answer most of what a parts supplier needs.

The StainlessLite range, model by model

The variants exist to solve different installation problems rather than to sell different levels of quality, and knowing which problem yours was bought to solve tells you a lot about the property. The standard indirect cylinder is the common case: a single coil heated by the boiler, sitting in an airing cupboard, serving a house or a converted flat with a system boiler.

Direct versions carry no boiler coil at all and are heated by immersion elements only. They turn up in flats with no gas appliance and in properties on electric heating. That distinction is the single most useful thing an owner can know, because if your cylinder is direct then no boiler fault can possibly be the reason you have no hot water. We attend calls every year where a boiler was stripped and tested for a fault that was never in it.

Beyond those two are shape and duty variants. A slimline version exists for the narrow cupboards you find in conversions. A horizontal version exists for lofts and low spaces. Solar versions carry a second coil, and are only worth having where that circuit actually exists. More recent additions are built around heat pump duty, which needs a far larger coil surface because the water reaching the coil is much cooler. There are also boosted variants for properties where the incoming main cannot deliver enough flow on its own, which answers a real London problem but adds a pump and its controls to the list of things that can fail.

• Indirect: heated by a boiler coil. The usual London installation.
• Direct: heated by immersion elements only, with no boiler involvement at all.
• Slimline and horizontal: shape variants for narrow cupboards and loft spaces.
• Solar: a second coil, useful only where a solar thermal circuit exists.
• Heat pump duty: a larger coil surface for lower flow temperatures.
• Boosted variants: for properties where the incoming main is weak.

How a StainlessLite handles expansion

StainlessLite uses a separate expansion vessel mounted on the cold feed, which is the conventional arrangement and, in our view, the more serviceable one. Water expands as it heats, the cylinder is sealed, and that expansion has to go somewhere. An external vessel is a visible component on a bracket that any competent plumber recognises on sight.

The practical advantage over designs that hold the air pocket inside the cylinder is that an external vessel is a commodity part. It can be checked, it can usually be replaced from the van, and the work is not tied to a manufacturer specific procedure that a stand in engineer might never have been shown. Over the twenty years and several changes of plumber that a cylinder actually lives through, that is worth more than it looks on installation day.

The trade off is one more component in an already crowded cupboard, and a wearing part rather than a permanent one. A vessel that has stopped doing its job announces itself the way most unvented faults do, with water appearing at the tundish when the cylinder reheats.

Water running from the tundish whenever the cylinder heats up means a safety device is passing or expansion has nowhere to go. Turn the cylinder heating off and get it looked at rather than putting a bucket under it.

The inlet control group is the part that matters most

On any unvented cylinder the small cluster of fittings on the cold feed does most of the work and causes most of the faults, and StainlessLite is no exception. That group typically contains a strainer, a pressure reducing valve that brings the incoming main down to what the cylinder is designed for, a check valve that stops hot water travelling back into the cold pipework, and an expansion relief valve that discharges to the tundish.

How those parts are arranged is the detail worth asking about, and it is where generations differ. A control group built from individual replaceable components means a failed pressure reducing valve is a cheap part and an hour of labour. A group supplied as a single moulded assembly is tidier and quicker to install, but when one element inside it drifts you can end up changing the assembly rather than the failed part. That is not a safety issue and not a criticism of the engineering. It is a serviceability point, and nobody thinks to ask it before a cylinder is chosen.

The separate temperature and pressure relief valve on the cylinder body is not part of that group and is not interchangeable with it. It is the last line of protection, and any discharge from it is a fault to diagnose rather than something to adjust or cap.

• Strainer: catches debris, and blocks more often in older London pipework.
• Pressure reducing valve: drifts or blocks, showing up as poor or unbalanced hot flow.
• Check valve: stops hot water backing into the cold side.
• Expansion relief valve: passes when worn, and sends water to the tundish.
• Temperature and pressure relief valve: separate, and never to be interfered with.

What actually fails on a Gledhill StainlessLite

The stainless vessel is the longest lived part, and in a properly serviced installation it outlasts several sets of valves and immersion elements. What we are called out to are the components attached to it, and a small number of them account for the large majority of calls.

The commonest is a wearing valve on the cold feed, reported as water at the tundish or as hot water that has lost its pressure while the cold taps are unaffected. Next is the immersion element, which fails in London mostly because scale has built up on it until it runs hot under its own insulating layer. Next again is the motorised valve on the heating side, which sends boiler heat to the cylinder coil and which, when it fails, gives the classic pattern of hot radiators and stone cold taps. That fault is not in the cylinder at all, yet it is the one most often used to sell a new one.

Two further items are worth naming because they are so often misread. A strainer that has silted up behind an inlet valve mimics a failing pressure reducing valve exactly. And a scaled coil does not fail outright, it just transfers heat more slowly, so the household concludes the cylinder is undersized. It usually is not.

• Inlet or expansion relief valves worn or drifted: water at the tundish, or weak hot flow.
• Immersion element scaled and burnt out: no hot water on a direct cylinder.
• Motorised valve on the heating side: heating fine, hot water absent.
• Blocked strainer: looks exactly like a failed pressure reducing valve.
• Scaled coil: slow recovery, commonly mistaken for an undersized cylinder.
• The stainless vessel itself: rare, and the one failure nobody can repair.

Can you still get parts for an older StainlessLite

For current StainlessLite Pro models, parts and service kits are ordinarily available and a replacement is a routine order. For earlier generations the answer splits along a line worth understanding before anyone tells you your cylinder is beyond help.

Standard plumbing parts remain straightforward. Expansion vessels, relief valves, immersion elements on a conventional screw in fitting and most inlet valves are either still available or have a recognised equivalent an experienced engineer can specify with confidence. Those are the parts that fail most often, which is why most repairs on an older StainlessLite are entirely ordinary jobs. Where it gets harder is anything proprietary to a discontinued model, such as a control assembly only ever supplied complete. Those are ordered rather than stocked and lead times vary. Nobody should tell you parts are unobtainable without reading the model number off the badge and checking.

What London hard water does to a StainlessLite

Almost the whole London supply area is hard water, and it is the biggest single factor in how any unvented cylinder ages here. Scale forms on heat transfer surfaces, which means the boiler coil and the immersion element, and those two surfaces determine how the cylinder behaves as it gets older rather than the steel around them.

A scaled coil slows recovery. The household notices that a second shower runs lukewarm where it never used to, blames the size of the cylinder, and is sometimes sold a bigger one to fix a problem that was never about capacity. A scaled element runs hot beneath its own deposit, which is precisely how elements fail early. Storing water far hotter than the household needs accelerates both and buys nothing that correct sizing would not have given you.

Where the cylinder lives changes the stakes. In a Victorian conversion with the cylinder in a first floor cupboard, everything underneath it is somebody else’s ceiling, so a weeping joint nobody noticed for a fortnight becomes a decorating job as well as a plumbing one. In a new build with liquid screed over underfloor heating, hot water and heating want different flow temperatures and the design has to separate them. In a purpose built block running a thermal store, none of this applies, because that is a different appliance again.

• Scale on the coil: slow recovery between draw offs, often misread as too small a cylinder.
• Scale on the element: the element runs hot under it and eventually burns out.
• First floor cupboard: small leaks turn into ceiling damage quickly.

Should you repair a StainlessLite or replace it

Repair it, unless the stainless vessel itself has failed. That is the honest answer and it holds far more often than replacement quotes suggest. A passing relief valve, a drifted pressure reducing valve, a blocked strainer, a burnt out immersion element and a failed motorised valve are all ordinary repairs on a cylinder with years of service left, and none of them are a reason to take the vessel out of the cupboard.

The genuine replacement case is a vessel that is weeping. Stainless cannot be patched, so once the vessel leaks the cylinder is finished whatever condition the rest of it is in. The other fair cases are a cylinder badly undersized for the way the household now lives, one where a proprietary part on a long discontinued model cannot be sourced in reasonable time, and one where the installation is wrong in ways that cannot be corrected around the existing unit.

What should stop you is a quote for a new cylinder produced without a diagnosis. If nobody has named the component that failed, nobody has established that the vessel is the problem, and replacing a repairable cylinder is the most expensive mistake available in an airing cupboard.

A weeping stainless vessel is a replacement. A failed valve, strainer, element or motorised valve is not. Establish which one you have before you accept any quote.

What to ask before anyone quotes you for a replacement

Begin with identification and diagnosis. Ask what model and capacity is on the badge, which component has been tested, and what the result of that test was. A quote that follows a named failed part is a different document from a quote that follows a glance at an old looking cylinder.

If you are genuinely replacing, the questions worth asking are about the next twenty years rather than about installation day. Whether the inlet controls are individual replaceable parts or a single assembly. Where the immersion element will physically withdraw to, because in London we regularly find cylinders set so close to a wall or a boxed in stack that the element cannot come out without dismantling joinery. Whether the mains flow rate and pressure have been measured, because an unvented cylinder is only as good as the supply feeding it. And who will service it annually, since one that is not serviced will repeat the same symptom until somebody does the step being skipped.

• What is the exact model and capacity on the data badge.
• Which component has been tested, and what was the result.
• Are the inlet controls individual parts or a single assembly.
• Is the immersion a conventional element or a proprietary one.
• Where will the element withdraw to in that cupboard.
• Has the mains flow rate and pressure been measured at the property.