Gledhill Cylinders Explained

What is a Gledhill cylinder

Gledhill is a hot water and heating manufacturer based in Blackpool, Lancashire, supplying British merchants and housebuilders for decades. What people call a Gledhill cylinder is usually one of two very different things. The first is a genuine unvented cylinder, a sealed stainless vessel of potable hot water fed off the incoming mains and heated by a boiler coil, an immersion element or both. The second is a thermal store, which holds heating water rather than drinking water and heats your mains supply as it passes through a heat exchanger.

We are an independent plumbing and hot water firm with twenty engineers. We are not an approved, authorised, accredited or official installer, service agent or partner of Gledhill or any other manufacturer, and nothing here is endorsed by them. We simply work on these units across London every week, and this is our own engineering view of them.

This page spends so long on identification because the wrong assumption here is expensive. Householders are quoted for an unvented cylinder replacement when they actually have a thermal store, or told a thermal store is beyond repair by somebody who has only ever worked on cylinders. Establishing which product is in the cupboard takes about a minute and changes every conversation after it.

• StainlessLite and StainlessLite Plus: the unvented stainless cylinder range.
• Torrent: open vented thermal stores, mains hot water without a sealed potable vessel.
• BoilerMate: thermal stores designed to work with a boiler, often with a control panel.
• Pulsacoil: electrically heated thermal stores, very common in London flats with no gas.

What is the difference between a Gledhill cylinder and a Gledhill thermal store

A cylinder stores the water that comes out of your taps. A thermal store stores water that never reaches your taps and uses it to heat your mains supply on the way past. That single difference drives everything else about how the two behave, how they are serviced and what they cost to put right.

In a StainlessLite or any other unvented cylinder, the vessel is under mains pressure and holds potable water. Because water expands when it is heated and the vessel is sealed, the installation needs an expansion vessel, a set of inlet controls on the cold feed and safety relief valves that discharge through a tundish to outside. That tundish and its discharge pipe are the giveaway. If you can see a small open gap in a copper pipe above the cylinder with a pipe running away from it, you are looking at an unvented cylinder.

In a Torrent, BoilerMate or Pulsacoil thermal store, the stored water sits at or near atmospheric pressure and is topped up from a small header arrangement in or on the unit. Your mains water only enters at the point of use, passing through a heat exchanger and arriving hot in seconds. There is no potable vessel under pressure, so normally no tundish, no inlet control group and no expansion vessel on the cold feed. What there usually is instead is a control panel, a pump, a blending valve and, on electric models, immersion elements.

Getting this wrong wastes money in both directions. A thermal store cannot be swapped for a cylinder without changing pipework and sometimes the incoming supply arrangement, and a cylinder job quoted at thermal store assumptions will miss most of the work.

How do I tell which Gledhill unit I have

Work through four checks in order and you will have the answer before anybody arrives: look for a tundish, look for a control panel, look at what heats it, and read the data plate.

Check one, the tundish. A small open air gap in the pipework above the unit, with a discharge pipe leading outside, means an unvented cylinder. No tundish and no discharge pipe means a thermal store in almost every case. Check two, the front panel. A moulded plastic fascia with buttons, lights or a rotary control belongs to a BoilerMate or a Pulsacoil, because thermal stores need active control of charging and blending. An unvented cylinder usually has nothing on the front but insulation and a data label.

Check three, the heat source. If the property has no gas supply at all, which is common in purpose built London blocks, and a tall white unit in a cupboard is producing mains pressure hot water, it is almost certainly an electric thermal store. A system boiler with a flow and return pair running into the unit points instead at a cylinder or a boiler fed thermal store. Check four, the data plate, normally on the front or side of the casing near the top. Photograph it. Model, capacity and serial number turn a later parts conversation into a short phone call.

• Tundish and discharge pipe: unvented cylinder, most likely StainlessLite.
• Control panel with lights or buttons on the front: thermal store, BoilerMate or Pulsacoil.
• No gas in the flat but mains pressure hot water: electric thermal store.
• Boiler flow and return plus a tundish: unvented cylinder with a coil.

What are the main Gledhill ranges

Four names cover almost everything we meet in London: StainlessLite, Torrent, BoilerMate and Pulsacoil. Knowing which family yours belongs to tells you more about your options than the individual model number does.

StainlessLite is the unvented cylinder range and the one that competes directly with the other mainstream British unvented cylinders. It is a stainless steel vessel with foamed insulation, an immersion boss, one or two coils depending on the model and a conventional inlet control group on the cold feed. Slimline versions exist for narrow cupboards, and twin coil versions exist for solar thermal or a second heat source. This is a conventional, serviceable unvented cylinder and the wearing parts on it are ordinary industry components.

Torrent is the thermal store family, delivering mains pressure hot water without a sealed potable vessel. BoilerMate is the boiler fed version. Pulsacoil is the electric thermal store, and in London it is everywhere: purpose built blocks from the nineteen nineties onward, all electric flats with no gas riser, and estates where one product was specified across hundreds of units at once. Several Pulsacoil generations exist, and they differ enough in controls and heat exchanger arrangement that identifying the exact model is worth doing before any parts are ordered.

What goes wrong with a Gledhill cylinder

On a StainlessLite, the failures sit in the fittings rather than in the steel, which is true of every well made unvented cylinder. In rough order of how often we attend them: the immersion element scales and burns out, the expansion vessel diaphragm perishes and the tundish begins to drip, the pressure reducing valve on the inlet drifts or sticks, the expansion relief valve starts to pass, the motorised valve on the heating side sticks or its switch fails, and the control thermostat fails. Every one of those is a replaceable part on a cylinder with years of life left in it.

On the thermal stores the fault list is different, because the complexity lives in the controls rather than in a pressure vessel. Pumps seize or lose their prime. Plate heat exchangers scale up in hard water and the hot water goes lukewarm at high flow rates. Thermostatic blending valves stick. Immersion elements on the electric models scale and fail, and on units with two elements the household often runs on one for months without realising, wondering why recovery has become so slow. Control boards fail, and that is where the age of the unit starts to matter.

What we do not see much of is early vessel failure on the StainlessLite range. The stainless work is sound. A vessel that eventually weeps cannot be patched or welded back into service, so that is a genuine replacement. The point is to establish that the vessel is what failed, and not accept a replacement quote for what turns out to be a valve.

A tundish that is discharging is a safety device doing its job and telling you something upstream has failed. Nobody should ever cap, plug or pipe away a discharging valve instead of finding out why it is discharging.

Can you still get parts for a Gledhill

For the StainlessLite range and for current thermal stores, parts are straightforward. For discontinued thermal store models, particularly older electric ones with proprietary control boards, availability is the single biggest factor in whether a repair is sensible, and it is the fair technical criticism of this range.

Take the cylinders first. StainlessLite wearing parts are barely manufacturer specific at all. The immersion element screws into a standard boss. The expansion vessel is a commodity potable water vessel. The inlet controls are the same families of valves used across the industry. Gledhill has also been sold through British merchants long enough that branch stock is generally good, which is a real advantage over brands reaching the UK through narrower distribution. An engineer with a well stocked van fixes most StainlessLite faults on the first visit.

The thermal stores are a different conversation and it is worth being honest about it. Pumps, blending valves, immersion elements and plate heat exchangers are all obtainable, sometimes as direct equivalents rather than branded parts. Control boards are the constraint. Once a generation has been out of production for a long time, boards stop being made and remaining stock becomes scarce, so the engineering question changes from how to repair it to whether the unit still earns its cupboard. That is not a safety point and not a criticism of the build. It is what happens to any appliance built around a proprietary board, and it is a reason to establish the model and check availability before committing to a repair.

• Immersion elements: standard boss, widely available.
• Expansion vessels and inlet valves on a StainlessLite: commodity merchant parts.
• Pumps, blending valves and heat exchangers on a thermal store: generally obtainable.
• Control boards on discontinued thermal store generations: the real availability risk.

How does London water treat a Gledhill

Hard, the same way it treats every hot water product here. Almost the whole London supply area is hard water, and the consequences for stored hot water are consistent regardless of badge: scale on the immersion element, scale on the coil, slower recovery over time and shorter element life than the same appliance would see in a soft water region.

On a StainlessLite the scale story is familiar. Deposits build on the element surface, that layer insulates the element, the element runs hotter than it was designed to and eventually burns out. Deposits on the coil reduce heat transfer, so reheat takes longer every year, and householders usually blame the boiler. Two decisions genuinely help. Specify an Incoloy or titanium sheathed immersion element rather than the cheapest copper one, and do not run the store hotter than the household actually needs, because every extra degree accelerates deposition on every heated surface.

On a thermal store the same chemistry attacks a more sensitive component. The plate heat exchanger is where your mains water meets the stored heat, its passages are narrow by design, and scale in those passages turns a strong shower into a disappointing one. A thermal store that used to be fine and now runs lukewarm when you open a second tap is usually a heat exchanger problem rather than a dead unit. Access is the other London variable, and it is nothing to do with the manufacturer: in Victorian conversions with the unit in a first floor cupboard we regularly find no room to withdraw an immersion element without dismantling joinery.

Should you repair or replace an older Gledhill

Repair whenever the failed component is available and the rest of the unit is sound. Replace when the stainless vessel has failed, or when a discontinued thermal store needs a control board that can no longer be obtained. Everything else is a judgement about how many more ordinary faults the unit is likely to hand you.

On a StainlessLite the decision is usually easy. A dead immersion, a perished expansion vessel, a drifted pressure reducing valve, a passing relief valve or a stuck motorised valve are all routine repairs that keep a good cylinder in service for years. The only automatic replacement is the vessel itself. Get a diagnosis from somebody qualified to work on unvented systems before accepting any replacement quote, because replacing a repairable cylinder is the most expensive mistake in this subject.

On an older thermal store, particularly an electric one in a flat, the honest answer depends entirely on the model and the specific fault. A pump, a blending valve, an element or a heat exchanger is worth doing. A board that no longer exists is not a repair at all, however willing the engineer is. That is the point at which a conversation about what to install instead becomes worth having, and it is a conversation that has to start with what the flat actually has: the incoming mains flow and pressure, whether there is gas, what the discharge arrangement could look like and what the building will allow.

• Failed immersion, expansion vessel, inlet valve or motorised valve: repair.
• Scaled plate heat exchanger on a thermal store: normally repair or exchange.
• Weeping stainless vessel: replacement, with no repair option.
• Unavailable control board on a discontinued model: replacement conversation.

What replacing a Gledhill cylinder involves

Diagnosis first, then a day of work in most London properties. Nobody should quote a replacement before establishing which component failed, because the difference between a valve and a vessel is the difference between a short visit and a full installation.

Where the steel has genuinely gone, the sequence is isolate and drain, disconnect the coil connections, the cold feed, the immersion and the discharge pipework, get the old unit out of the cupboard, set the new one, remake every connection, fit and set the inlet control group, run the discharge correctly, refill, vent, commission and test. What drives the cost is the specification of the cylinder you choose, how much pipework has to be remade because the new connection positions differ from the old ones, whether the discharge arrangement needs redoing and how bad the access is. Our rate lives on our pricing page rather than buried in an article.

Swapping a thermal store for an unvented cylinder is a bigger piece of work again, because the two products want different things from the property. A cylinder needs a mains supply capable of sensible flow at pressure, a safe discharge route to outside and space for a vessel plus its controls. Plenty of London flats can take one and some cannot. Access surprises people most: a unit in a ground floor utility is a very different day from one at the top of a Victorian staircase with a turn in it, which is why our first question on a replacement is usually where the unit sits rather than which brand is going back in.