Telford Tempest Cylinders

What is a Telford Tempest cylinder

A Tempest is an unvented stainless steel hot water cylinder. Unvented means the store is sealed and fed directly from the incoming cold main, so every hot tap in the property runs at roughly mains pressure and there is no cold water tank in the loft. The vessel is duplex stainless steel, a grade chosen because it tolerates the chloride content of a mains fed store and needs no sacrificial anode inspected or renewed.

The Tempest name covers a family rather than a single product. Within it there are indirect models heated by a coil from the boiler, direct models heated only by immersion elements, slimline and horizontal shapes for awkward spaces, twin coil versions for solar thermal, and versions built for heat pumps with a far larger coil. They share the vessel, the external expansion arrangement and the control philosophy, and they differ in the things you cannot change afterwards.

What makes the range distinctive is not the steel, because most serious unvented cylinders sold here use a comparable vessel. It is everything around the steel. Expansion lives outside the cylinder in an ordinary replaceable vessel, the immersion screws into a standard boss and takes a merchant element, and the inlet controls are separate components rather than one sealed assembly. None of that is glamorous and all of it decides what a repair looks like in year twelve.

How do I know which Telford Tempest I have

Read the data plate on the side of the cylinder. It carries the model reference, the nominal capacity in litres and a serial number, and it is the only reliable identification. Photograph it before you speak to anybody about a repair, a service or a replacement, because almost every wasted visit to a cylinder starts with somebody guessing the model from the pipework.

The first thing the plate settles is indirect against direct. An indirect cylinder has a coil inside it fed by the boiler, so it has flow and return pipes running to the cylinder as well as cold in and hot out, and it usually has an immersion element as a backup. A direct cylinder has no coil and is heated only by its elements. That distinction changes the diagnosis completely: no hot water on an indirect cylinder can be a heating side fault, while on a direct cylinder it is almost always electrical.

The second thing to establish is what the cylinder physically is. Not every hot water vessel in a London airing cupboard is an unvented cylinder. Purpose built blocks on a communal system often hold a thermal store instead, which looks similar, behaves differently and fails differently. An old vented copper cylinder fed from a loft tank is a different appliance again. If the plate is unreadable or missing, an engineer can tell them apart in minutes by what is plumbed to the vessel, and that is worth doing before any quote is accepted.

Photograph the data plate. The model reference, capacity and serial number are what let anybody order the right parts first time.

What is in the Tempest range

Six variants cover almost everything we meet. Indirect models, heated by a boiler coil with an immersion as backup, are the common domestic choice. Direct models, heated by elements alone, appear in flats with no boiler. Slimline models trade diameter for height, horizontal models lie down in a roof space, twin coil models take solar thermal, and heat pump models carry a much larger coil for low flow temperatures.

Those choices are made at the point of purchase and cannot be revisited. You cannot add a coil to a direct cylinder, you cannot turn a standard coil into a heat pump coil, and a horizontal cylinder cannot be stood up. The most expensive mistake in this whole subject is buying the wrong variant because nobody asked what the property would be doing in five years, then trying to correct it with controls afterwards.

If a heat pump is anywhere in the plan, say so before anything is ordered. A heat pump delivers water at a much lower flow temperature than a gas boiler, so the coil needs far more surface area to move the same energy into the store. A boiler specification cylinder connected to a heat pump reheats slowly, and no amount of adjustment fixes an undersized coil later.

• Indirect: boiler coil plus immersion backup, the usual domestic fit.
• Direct: immersion elements only, no boiler coil.
• Slimline: narrower body, taller, for tight cupboards.
• Horizontal: lies flat in a roof space or above a ceiling.
• Twin coil: lower coil for solar thermal.
• Heat pump: much larger coil for low flow temperatures.

Where Telford Tempest cylinders turn up in London homes

Most Tempest cylinders we attend in London are replacements rather than original fittings. The typical job is a Victorian or Edwardian conversion where the old vented cylinder in the first floor cupboard has reached the end of its life and the household wants mains pressure hot water without keeping a tank in the loft. The slimline and horizontal shapes exist for exactly that, where the cupboard was built around a cylinder nobody makes any more and the doorway cannot be widened.

The second place they appear is new build houses and flats, often alongside underfloor heating laid in liquid screed. There the cylinder was specified with the rest of the system and the pipework around it is usually generous and accessible, which makes servicing straightforward.

Purpose built blocks are the case to be careful with. Plenty run a communal heating system with a thermal store in each flat rather than an unvented cylinder, and a thermal store is not a Tempest and does not take Tempest parts. Loft conversions are the other common context: a new shower room at the top of the house needs a pressure the old vented system cannot give it, which is a good reason to go unvented as long as somebody measured the incoming mains first. An unvented cylinder of any brand is only ever as good as the supply feeding it.

What goes wrong with a Telford Tempest

The wearing parts around the vessel fail long before the vessel does. Across the Tempest cylinders we attend, the recurring faults are an inlet pressure reducing valve that has drifted, a passing expansion relief valve, a passing temperature and pressure relief valve, a perished expansion vessel diaphragm, a burnt out immersion element and a failed motorised valve. Every one is a repair using a part an engineer can carry.

The single most common call is a dripping tundish. The tundish is the open gap in the discharge pipe, and water running through it means a safety valve is passing. On a Tempest the usual culprits are a spent expansion vessel diaphragm, a worn expansion relief valve or a pressure reducing valve that is no longer holding the inlet where it should. It is ordinary diagnostic work for somebody who knows the cylinder. What it is never is a plumbing nuisance to be silenced, and anybody suggesting the discharge be capped rather than investigated should be shown the door.

The second most common is a dead immersion element, which in London is usually a scale story rather than an age story. The genuinely terminal fault is a weeping stainless vessel. It cannot be patched, and it ends the cylinder. In our experience that is uncommon on a duplex vessel that has been serviced and has not been run permanently hotter than the household needed.

A dripping tundish is a safety valve telling you something upstream has failed. It is a diagnosis job, never a reason to cap the discharge pipe.

Why a Tempest is straightforward to repair

Because almost nothing on it is proprietary. The immersion boss takes a standard screw in element bought from any merchant. The inlet control group is a set of discrete components, so a passing expansion relief valve is a valve change rather than the replacement of a whole moulded assembly. The expansion vessel is an ordinary commodity vessel on the cold feed. There is no control board that has to be matched to a serial number and no sealed cartridge that turns a small fault into a large invoice.

That matters more than it sounds. A cylinder has to survive two changes of ownership and four different plumbers, and every proprietary component in it is a dependency on the manufacturer still trading and still supporting that model a decade on. Where everything else is close, the cylinder built from stock parts is the one that stays repairable.

It also shortens the visit. A cylinder built from standard components is often diagnosed and fixed on the same call, because the likely parts are already in the van. One that needs a branded item ordered in turns a two hour job into a second appointment with no hot water in between.

How does a Tempest cope with London hard water

Hard water does more damage to a hot water cylinder in London than any difference between brands. Almost the entire London supply area is hard, and scale settles on the two hottest surfaces in the appliance: the outside of the boiler coil and the sheath of the immersion element. Scale insulates. An insulated coil reheats the store slowly, and an insulated element runs hotter than it was built to run and eventually cooks itself.

A Tempest is no more immune to this than anything else. What it does is make the consequences cheap to deal with, because the element that scales is a stock part and the coil sits inside a vessel that is otherwise in good order. Two decisions at the point of purchase make a real difference. Specify an Incoloy or titanium sheathed element rather than the cheapest copper one, because a better sheath tolerates scaling for far longer. And do not set the store temperature higher than the household actually needs as a way of masking a cylinder that is too small, because running hot permanently accelerates scaling on both surfaces and buys nothing that correct sizing would have given you anyway.

The third point is physical and specific to London housing. An immersion element withdraws in a straight line and needs real clearance to come out, 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 for good.

What happens when a Telford Tempest is serviced

A proper annual service is an inspection and exercise of every safety and control component, not a glance and an invoice. The engineer checks and operates the temperature and pressure relief valve and the expansion relief valve, inspects the discharge pipework and the tundish, checks the external expansion vessel and its diaphragm, confirms the inlet control group is holding the cylinder where it should be, inspects the immersion and its wiring, and looks over the vessel and its connections for any weeping.

Because a service kit is published for the range, the sensible thing when wearing parts are due is to change them during the visit rather than book a second call. That is the quiet advantage of a cylinder assembled from discrete parts: the annual service can be genuine maintenance instead of a tick list.

There is a second reason to keep it up. Manufacturer warranties on unvented cylinders are conditional on annual servicing and on the paperwork being retained, and that applies across this market rather than to one brand. We have no part in any manufacturer warranty and make no claims about ours, but a long warranty quoted without a word about its service condition is worth less than the person quoting it would like you to believe. Keep the certificates.

What size Telford Tempest does a London home need

Size the cylinder around simultaneous demand and reheat, not around the number of bedrooms. A two or three bedroom conversion with one bathroom and a system boiler is well served by a mid sized indirect Tempest with a standard coil. A family house with two bathrooms that both get used at eight in the morning needs both more volume and a higher output coil, because the complaint in those houses is almost never that the cylinder ran out once, it is that it took too long to come back.

Measure the incoming main before anything is ordered. An unvented cylinder distributes whatever the main can deliver and cannot invent flow that is not there, and plenty of London properties, particularly upper flats on long shared supplies, have less than their owners assume.

Then check the cylinder can physically get in. Doorway widths, stair turns, cupboard depth and ceiling height decide whether the slimline or horizontal variant is the right answer, and access is the commonest cause of a replacement day going wrong in a Victorian house.

• One bathroom, system boiler: mid sized indirect with a standard coil.
• Two bathrooms with overlapping use: more volume and a higher output coil.
• Electric only: a direct model, sized around the off peak window.
• Heat pump now or later: the heat pump variant, decided before ordering.
• Tight access: slimline or horizontal, measured before the order goes in.

Should a Telford Tempest be repaired or replaced

Repair is the right answer far more often than the quote in your inbox implies, and on a Tempest particularly, because the parts are standard. A passing relief valve, a drifted pressure reducing valve, a spent expansion vessel, a dead element or a failed motorised valve are all repairs on a cylinder that may have many years left in the steel. Replacing a repairable cylinder is the most expensive mistake available in an airing cupboard.

Replacement is the honest answer in a small number of cases. A weeping or corroded stainless vessel is terminal. A cylinder so undersized, or so badly positioned that nothing on it can be serviced without dismantling joinery, is a fair replacement argument even when nothing has actually failed. Beyond those, ask for the diagnosis before you accept the quote.

What drives the cost of a cylinder replacement is the job rather than the badge on the front. Whether the old cylinder can get out of the cupboard and the new one in. Whether the pipework has to be rerouted. Whether a compliant discharge route to outside already exists or has to be created, which in an upper flat can be the single biggest item in the work. Whether the incoming main can feed an unvented cylinder at all. And what the household does for hot water while the work happens. Our rates are set out on our pricing page rather than buried in an article.

• Repairable: relief valves, pressure reducing valve, expansion vessel, element, motorised valve.
• Terminal: a weeping or corroded stainless vessel.
• Judgement call: wrong size, or a position that makes servicing impossible.
• Cost drivers: access, pipework, the discharge route and the incoming main.