Telford Cylinders Explained

What is a Telford cylinder

Telford is a cylinder manufacturer based in Shropshire that builds both copper and stainless steel hot water cylinders for the UK market. When somebody says they have a Telford cylinder in a London property they almost always mean a Tempest, which is the unvented stainless steel range: a sealed, mains pressure hot water store fed directly off the incoming cold main, with an inlet control group on the cold feed and an external expansion vessel taking up the expansion when the water heats.

The vessel is duplex stainless steel, which is the right material for an unvented store: it resists the chloride stress corrosion that ends the life of lesser grades and needs no sacrificial anode. In that respect a Tempest sits in the same category as every other serious unvented cylinder sold here. The differences between brands are not about the steel. They are about what happens around it.

The rest of the catalogue turns up often enough to be worth knowing: open vented stainless cylinders for systems still fed from a loft tank, traditional copper vented cylinders for like for like swaps, and heat pump versions of the Tempest with a much larger coil. If you are unsure which you have, the data plate on the side of the cylinder is the only reliable answer.

• Tempest: the unvented duplex stainless range, the one most Londoners mean.
• Vented stainless models: for systems still fed by a cold water storage tank.
• Copper vented cylinders: like for like replacements in older installations.
• Heat pump versions: same family, far larger coil, specified at purchase.

Where Telford cylinders turn up in London homes

Telford cylinders appear most often where somebody made a considered choice rather than accepted whatever the merchant had in stock. In practice that means replacement jobs in Victorian and Edwardian conversions, where the old vented cylinder in the first floor cupboard has come to the end of its life and the household wants mains pressure hot water without the loft tank. The Tempest range includes slimline and horizontal shapes, and those solve a genuine London problem: cupboards built around a cylinder that no longer exists, in a flat where nobody can widen the doorway.

They also turn up in new build houses and flats, often alongside liquid screed floors and underfloor heating. Purpose built blocks are a more mixed picture: plenty run a communal system with a thermal store in each flat rather than an unvented cylinder, and a thermal store is a different appliance with a different failure pattern. Do not let anybody quote a Tempest replacement until it is clear which of the two you have.

The last common place we find them is the loft conversion, where a new shower room at the top of the house needs a pressure the old vented system cannot give it. That is a good outcome as long as the incoming mains was measured first, because an unvented cylinder of any brand is only as good as the supply feeding it.

How a Telford Tempest is actually built

The four things that decide whether you will be pleased with an unvented cylinder in year twelve are the vessel material, how expansion is handled, whether the immersion is a standard element, and whether the inlet controls are separate parts. A Tempest scores well on all four, and that is the whole argument for it.

Expansion is handled by an external vessel on the cold feed. That is the less clever of the two approaches used in this market and we prefer it anyway, because the vessel is a separate commodity component. When its diaphragm eventually perishes, an engineer fits another from the van and leaves. Nothing about that repair depends on Telford still supporting the model, still trading, or still making the part. For an appliance that has to survive two changes of ownership and four different plumbers, boring replaceability beats elegance.

The immersion boss is a standard screw in thread, so the element is a merchant part rather than a branded one, and any engineer carries the spanner. The inlet control group is assembled from discrete components, each with its own part number, so a passing expansion relief valve is a valve change rather than a whole assembly change. Connection positions are sensible and there is a proper service kit available for the model, which tells you the manufacturer expects the cylinder to be looked after rather than discarded.

• Duplex stainless vessel, no sacrificial anode to inspect.
• External expansion vessel, replaceable as an ordinary part.
• Standard screw in immersion boss, standard element.
• Inlet control group of individual parts, not one moulded unit.
• Slimline, horizontal and heat pump variants for awkward installations.

What actually fails on a Telford cylinder

The vessel is almost never the problem. On the Tempest cylinders we attend across London, the failures are overwhelmingly on the wearing parts around the outside: the pressure reducing valve on the inlet, the expansion relief valve, the temperature and pressure relief valve, the expansion vessel diaphragm, the immersion element and the motorised valve on the heating side. Every one of those is a repair, not a replacement, and every one of them is a standard part on this cylinder.

The most common single call is a dripping tundish. That is the discharge pipe doing its job, telling you a safety valve is passing water. On a Tempest the usual causes are a failed expansion vessel diaphragm, a worn expansion relief valve or an inlet pressure reducing valve that has drifted out of adjustment. It is ordinary work for an engineer who knows the cylinder. What it is not is a reason to cap the discharge, and anybody who suggests plugging a discharging safety valve rather than finding out why should be sent away.

The second most common is a dead immersion element, and in London that is usually scale rather than age. Scale builds on the element sheath, the scale insulates it, the element then runs hotter than it was designed to and eventually burns out. The good news on a Telford is that the element unscrews and is replaced with a stock part on the same visit. The genuinely terminal failure is a weeping stainless vessel, which cannot be patched and ends the cylinder. It is also, in our experience, rare on a duplex vessel that has been serviced and not run permanently hotter than the household needs.

A dripping tundish is a symptom, never a nuisance to be silenced. It means a safety valve is passing and something upstream needs investigating.

Telford Tempest compared with a Megaflo

Megaflo Eco is the market leader by name recognition and it is a well made cylinder with a sound duplex stainless vessel and a wide dealer network. Nobody with one should feel badly served. The honest technical comparison comes down to two design decisions where Telford takes the more serviceable route and Megaflo takes the more integrated one.

The first is expansion. Megaflo holds an air pocket inside the vessel behind an internal baffle instead of fitting an external expansion vessel. That is tidier: nothing hangs off the pipework and there is no external diaphragm to perish. The trade off is that the air pocket is gradually absorbed into the water, and restoring it is a manufacturer specific procedure carried out at the annual service. It is straightforward for an engineer who has done it before. It is also precisely the step that gets skipped when a cylinder is serviced by whoever quoted lowest that year. Telford's external vessel needs no special procedure and fails visibly.

The second is the immersion. Megaflo uses a branded immersion arrangement rather than a plain screw in element, so the replacement is a manufacturer part. That is not a defect and it is easy to change with the part in hand. It is a dependency, and dependencies turn a two hour repair into a three day wait once a model is out of production. Telford takes a merchant element.

Set against that, Megaflo is more widely stocked and far more engineers have worked on one, and in a block where several flats share the same cylinder that familiarity is worth something. Our preference for Telford is about long term serviceability rather than build quality, and we fit Megaflo without complaint where a household wants one.

• Expansion: Telford external and replaceable, Megaflo internal and procedure dependent.
• Immersion: Telford standard screw in element, Megaflo branded part.
• Vessel: both duplex stainless, and neither is the usual failure.
• Availability: Megaflo is more widely stocked and more widely familiar.

How Telford cylinders cope with London hard water

Almost the whole London supply area is hard, and hard water is harder on a hot water cylinder than any brand difference. Scale deposits on the coil and on the immersion element, and on both it acts as an insulating blanket. The result is slower reheat, a boiler or immersion working harder for the same hot water, and eventually an element that cooks itself. A Telford is no more immune to this than anything else, but it does make the consequences cheaper to deal with, because the element that scales is a stock part and the coil is inside a vessel that is otherwise holding up well.

Two specification choices are worth making at the point of purchase rather than regretting later. Specify an Incoloy or titanium sheathed immersion element rather than the cheapest copper one, because a better sheath tolerates scaling far longer. And do not set the store temperature higher than the household actually needs as a way of compensating for a cylinder that is too small or a coil that is too modest, because running hot permanently accelerates scaling on both surfaces and buys nothing that correct sizing would not have given you for free.

The other London point is physical. An element needs real room to withdraw, and in a Victorian conversion the cylinder is usually boxed into a first floor cupboard with joinery built tight around it. Ask the installer to show you where the element will come out to. If the answer involves dismantling a cupboard, the position is wrong and the cheapest repair on this appliance has just been made expensive.

Scale is the main enemy of any London cylinder. An Incoloy or titanium element and a sensible store temperature will do more for its life than the badge on the front.

What happens when a Telford cylinder is serviced

An annual service on a Tempest is a proper inspection of the safety and control components, not a glance and an invoice. The engineer checks and exercises the temperature and pressure relief valve and the expansion relief valve, inspects the discharge arrangement and the tundish, checks the external expansion vessel and its diaphragm, checks the inlet control group is doing its job, inspects the immersion and its wiring, and looks over the vessel and connections for any sign of weeping.

A service kit is available for the range, so where wearing parts are due the sensible thing is to change them during the visit rather than on a second call out. That is another quiet advantage of a cylinder built from discrete parts: the service is real maintenance rather than a checklist exercise.

Servicing matters for a second reason. Manufacturer warranties on unvented cylinders are conditional on annual servicing and on the paperwork being kept, and that applies to every brand in this market. We have no part in any manufacturer's warranty, but a warranty quoted without a word about the service condition is worth less than the person quoting it wants you to think. Keep the records.

Should a Telford cylinder be repaired or replaced

Repair is the right answer far more often than the quote in your inbox suggests, and on a Telford especially, because the parts are standard. A passing relief valve, a drifted pressure reducing valve, a perished expansion vessel diaphragm, a dead element or a failed motorised valve are all repairs on a cylinder with years left in the steel.

Replacement is the honest answer in a small number of situations. A weeping stainless vessel is terminal, because it cannot be patched and no amount of healthy valves changes that. A cylinder so undersized or so badly positioned that the household has never been happy with it is a replacement argument even when nothing has failed.

What drives the cost of a replacement is not the badge. It is the physical job: whether the old cylinder can get out of the cupboard and the new one in, whether the pipework needs rerouting, whether a proper discharge route to outside exists or has to be created, whether the incoming mains can actually feed an unvented cylinder, and what the property does for hot water while the work is happening. Get a diagnosis before you accept a replacement quote, because replacing a repairable cylinder is the most expensive mistake available in an airing cupboard.

• Repairable: relief valves, pressure reducing valve, expansion vessel, immersion, motorised valve.
• Terminal: a weeping or corroded stainless vessel.
• Judgement call: a cylinder that is the wrong size or in the wrong place.
• Cost drivers: access, pipework, discharge route and the incoming mains, not the brand.

Would we fit a Telford cylinder

Yes, and we do, more often than any other brand. In a two or three bedroom conversion with one bathroom and a system boiler, a Tempest in the mid sized range with a standard coil, an Incoloy element and the mains measured beforehand is a straightforward, sensible installation that will be easy to live with. In a family house with two bathrooms and simultaneous demand, the answer is more volume and a higher output coil rather than simply more litres, because the complaint in those houses is almost never storage and almost always recovery between showers.

If a heat pump is in the plan now or in five years, say so before anything is ordered and buy the heat pump rated version. A heat pump delivers a much lower flow temperature, so the coil has to be far larger to move the same energy, and no controls tuning fixes an undersized coil afterwards. This is the specification mistake we see most often across every brand, not just this one.

None of that makes Telford the only right answer. Gledhill, OSO and Albion are easy cylinders to live with for the same reasons, and a properly serviced Megaflo will give a household years of trouble free hot water. But where everything else is close and one cylinder takes stock parts while the other ties you to a manufacturer, choose the one any engineer can fix. That is the whole case for Telford.