Gledhill Pulsacoil Explained

What is a Gledhill Pulsacoil?

A Pulsacoil is a self contained electric hot water unit built around a thermal store. Inside the cabinet there is an insulated vessel of water, a small cistern on top that keeps it topped up, immersion heaters, a pump, a heat exchanger and a control board. The vessel water is the battery, heated overnight on an off peak rate and giving that heat away through the day.

Open a hot tap and cold mains water enters the unit, a flow switch notices, the board starts the pump, and store water circulates across a heat exchanger while your mains water travels the other way through it. The water you wash in was cold mains a few seconds earlier and never touches the stored water.

Gledhill designed the range for flats where a gas boiler was not an option, which is why so many purpose built London blocks have one standing in a kitchen or hall cupboard. Our page on how a Pulsacoil works covers the internals component by component. This page is about the model generations and what happens when one gets old.

• It is electric. No gas, no flue and no boiler behind it on the great majority of installations.
• It runs at mains pressure on the hot side, because what leaves the tap is mains water that has just been heated.
• The store is open vented and not pressurised, so it is not an unvented cylinder and is not treated as one.
• It is factory built, so almost everything inside is specific to the model.

Why a Pulsacoil is not a normal hot water cylinder

The difference that matters is what is being stored. A cylinder stores the actual hot water you will use, so opening the tap lets that stored water out. A Pulsacoil stores heat and manufactures your hot water on the spot as you draw it. Everything else follows from that one design choice.

It means a Pulsacoil has moving and electrical parts between the store and your tap. A cylinder needs nothing to work when you open the tap, because pressure and gravity do the job. A Pulsacoil needs the flow switch to notice you, the board to respond and the pump to run. If one of those is not working, the store can be full of heat while your shower runs cold.

It also means the store runs hotter than a cylinder would, because the hotter the store, the more usable hot water a fixed volume of tank delivers before it is exhausted. The outlet therefore usually carries a blending valve to bring the delivery temperature back down, and the store is a hot, scale forming environment by design.

And the failure mode is different. A cylinder that fails tends to leak or stop heating. A Pulsacoil often still heats perfectly well while failing to deliver, or loses performance so gradually that nobody can say when it started. Those are diagnostic problems rather than obvious breakages.

Which Pulsacoil model do I have?

Check the badge on the front panel or inside the door and photograph it before you ring anybody. The model name and any serial number decide what the fault codes mean, which parts are available, and whether a repair is realistic at all. An engineer who knows the range reads more from that photograph than from ten minutes of description.

Two practical consequences follow. A part from one generation will not fit another, and even a similar looking component is often not interchangeable. And what a symptom means depends on the generation. On an early unit, no pump activity when the tap runs points straight at the flow switch or the pump. On a later unit the board may be refusing to start the pump deliberately because a sensor is reading something it does not like, and swapping the pump would achieve nothing.

• Pulsacoil and Pulsacoil 2000: early generation, mechanical flow switch, direct switching board.
• Pulsacoil III: the most common in older London blocks, same basic architecture, very large installed base.
• Pulsacoil A Class: sensor based control with a display, so faults present as codes.
• Pulsacoil Eco: later sensor controlled unit, different board and different parts again.
• Pulsacoil BP and Stainless Lite: heat comes from a separate or communal source rather than from immersion elements in the cabinet.

If the badge is missing or unreadable, do not guess from the cabinet shape. Several generations share similar casings, and ordering parts on a visual guess is how a repair turns into two visits instead of one.

Why do so many plumbers refuse to work on a Pulsacoil?

Because most plumbers rarely see one, and it does not behave like anything else they work on. A Pulsacoil is an electric appliance with a control board, a pump, sensors and a heat exchanger, dressed as a hot water tank. A plumber whose day is boilers and cylinders opens the panel, finds nothing they recognise, and sensibly decides it is not their job.

Three specific things push the work away. The controls are proprietary, so there is no generic fault finding routine and no substituting a standard part from the van. Diagnosis is mostly electrical, a meter and a sequence of tests rather than draining a tank. And the parts are model specific and must be identified correctly before they are ordered, which makes an unfamiliar engineer reluctant to commit to a fix they cannot finish on the day.

None of that makes the unit a bad appliance. A Pulsacoil that is charging properly, with a clean heat exchanger, delivers hot water at mains pressure perfectly well. The fair criticism of any integrated proprietary unit is that serviceability depends on parts continuing to be supplied and on engineers continuing to learn the range.

The practical effect is that the first firm you call may not be the right one. Ask on the phone whether they work on thermal stores and on your model. Our Pulsacoil repair page sets out what we look at and what is useful to have ready before an engineer attends.

What usually fails on a Pulsacoil

The fault list is short and fairly predictable, which is the advantage of a unit built to one design. An engineer works through it cheapest and quickest first.

The most common root cause in London is scale, and it attacks two components at once. On an immersion element it builds a crust that stops the element shedding heat into the water, so the element runs hotter than it should and eventually fails. Inside a plate heat exchanger it coats the plates and narrows the waterways, so less heat crosses and the hot flow drops. A unit that has quietly lost performance has usually lost it in both places, which is why renewing one and leaving the other brings the same complaint back.

The other recurring theme is that a hot store and a cold tap are not a contradiction. If the flow switch has stuck or the pump has seized, nothing tells the unit you have opened a tap, or nothing circulates when it does, and the store stays hot and useless. Mention that symptom on the phone, because it narrows the job considerably.

• No power to the unit, a tripped breaker, or the off peak circuit tripped separately. Checked first because it costs nothing.
• Immersion element failed or heavily scaled, so the store never charges overnight.
• Immersion thermostat failed, or the manual reset overheat cut out tripped for a reason that needs finding rather than resetting.
• Flow switch stuck, so the pump never starts and the hot tap runs cold from a hot store.
• Pump seized or failed. Same symptom, different cause.
• Plate heat exchanger scaled. Lukewarm water and reduced hot flow that got worse slowly.
• Control board failed. This is where model and parts availability usually decide the outcome.
• Float valve in the top cistern stuck, giving an overflow that looks exactly like the unit leaking when it is not.

Water running from an overflow pipe outside, or pooling under the unit, needs attention rather than watching. A thermal store holds a large volume of very hot water, and a flat above other flats is the worst place to let that develop.

Why London water is hard on a Pulsacoil

Almost the whole London supply area is hard water, and a thermal store is close to the worst appliance to ask hard water to live in. Scale comes out of solution faster the hotter the surface, and a Pulsacoil runs its store hotter than a cylinder by design. The hottest surfaces are the immersion elements, so scale forms there first and thickest.

The heat exchanger is the second casualty and the one people notice. Its whole job is to move heat across thin plates with narrow waterways, and a scale layer is an insulator sitting exactly where you least want one. Flow drops and delivery temperature drops, and because it happens over months the household adjusts without registering it. The moment of realisation is usually the second shower of the morning going cold.

This is chemistry meeting a hot surface rather than a fault. Our page on hard water and hot water cylinders in London covers what the same water does to conventional cylinders, and the pattern is the same even though the components differ.

Can you still get Pulsacoil parts?

It depends on the generation, and this is the question that decides whether a repair happens. Parts for the later sensor controlled units are generally the easier proposition. The earliest generations are the harder one, because manufacturers do not support discontinued products indefinitely and boards are the component that runs out first.

Some parts are not really Pulsacoil parts at all. Immersion elements, thermostats and pumps are components used across the industry, so there is often a route to a correct equivalent. Boards are the opposite. They are proprietary, they are what makes one generation different from another, and there is no equivalent to fit.

That is why diagnosis matters more on these units than on almost anything else in a flat. Whether your unit is repairable is not a general fact about Pulsacoils, it is a fact about your model and the component that has failed. A scaled heat exchanger and a dead board on the same unit lead to completely different conversations.

Should you repair a Pulsacoil or replace it?

Repair while the failed component is available and the rest of the unit is sound. Replace when the board has gone on a generation that no longer has boards, when the store vessel is leaking, or when two or three separate failures inside a couple of years have made the pattern clear.

Separate wear items from terminal faults. Elements, thermostats, flow switches, pumps and float valves wear out on any unit of any age, and replacing one is ordinary maintenance. A failed board on an unsupported generation, or a leaking store, is different. Those are the faults that end a unit.

There is a timing argument too. Replacing on your own schedule means the cupboard can be measured, the supply checked and the route worked out in advance. Replacing on the day the old one fails means doing all of that while the household has no hot water. Our page on whether it is worth repairing an old cylinder works through the same judgement for conventional cylinders.

What replacing a Pulsacoil in a London flat actually involves

The decision is made by the building, not by preference. In a block with no gas supply the realistic options are a like for like thermal store, a modern electric equivalent, or an unvented cylinder with immersion heating where the incoming mains can support it.

Mains supply is what catches people out. Both a thermal store and an unvented cylinder deliver mains water, so both are excellent on a strong supply and disappointing on a weak one. Measure the incoming flow rate at the flat rather than assume it.

The physical job is often the bigger constraint. These units live in cupboards, frequently on upper floors reached by a communal stair with no lift, and the old one has to come out whole or be broken down in place. In Victorian conversions the cupboard is a first floor box built around whatever was fitted decades ago, and the new unit has to fit through its door rather than merely inside it. In purpose built blocks the space is usually known and the route is the awkward part.

What drives the cost of a replacement, in general terms, is the unit specified, the state of the existing pipework and electrical supply, how much distribution pipework needs altering, the access, and whether the building requires notice for the work. Our hot water cylinder replacement page covers how the specification is arrived at.

• Confirm what the block can supply. Gas, electric only, or a communal heat source.
• Measure the incoming mains flow and pressure before any unit is specified.
• Measure the cupboard, its door, and the route in from the street.
• Check the electrical supply, since a different unit may not draw the same current.
• Ask the freeholder or managing agent whether notice is required.

What to check before you call an engineer

A worthwhile five minutes, because a fair share of Pulsacoil calls turn out to be a unit working as designed while being asked for more hot water than one overnight charge provides. None of the checks below involve opening anything electrical or removing a panel.

The most useful thing you can do is describe the pattern accurately. Genuinely hot water that then fades means the unit is heating and delivering correctly, so the question is capacity or timing. Never more than lukewarm is a fault. Stone cold at every tap all day is usually electrical. Those three descriptions send an engineer down three different paths before arriving.

• Photograph the model badge on the front panel or inside the door.
• Check the fused spur or breaker feeding the unit, and whether the off peak circuit has its own breaker that tripped alone.
• Press the boost switch and wait an hour. Hot water afterwards means the store was empty rather than broken.
• Confirm the off peak hours on the meter or time switch. Meter swaps and power cuts quietly change them.
• Listen at the unit while a hot tap runs. The pump should start within seconds, and silence is useful to pass on.
• Check the cold flow at the kitchen tap. Weak cold means weak hot, which is a supply question rather than a Pulsacoil one.

If none of those change anything, the fault is inside the unit. Beyond that point you are dealing with high current immersion circuits and a vessel of water hot enough to scald, and it needs somebody qualified with the covers off.