Pulsacoil Repair in London

How a Pulsacoil works, and why that changes the fault list

In a normal hot water cylinder, the water in the tank is the water that comes out of your tap. In a Pulsacoil it is the other way round. The tank is full of stored water that stays in the unit permanently, heated by immersion heaters, usually overnight on an Economy 7 rate. When you open a hot tap, mains cold water runs through a plate heat exchanger, a pump pushes the hot stored water through the other side of that plate, and the heat crosses over. You get hot water on demand, at mains pressure, from a tank that is never under pressure itself.

The store is open vented. There is a small feed cistern built into the top of the unit with a float valve and a vent pipe, which is why a Pulsacoil has no expansion vessel, no pressure relief valve and no tundish, and why it is not an unvented cylinder in the sense the building regulations use that word. What it does have is electrics, a circulating pump, sensors and a control board, and those are the parts that fail.

So the diagnostic question on a Pulsacoil is never just "is the tank hot". It is "is the tank hot, and if it is, is the unit succeeding in moving that heat into the water you are trying to draw". Plenty of Pulsacoils with a scalding hot store deliver cold water at the tap, because the pump is not running or the plate is blocked. An engineer who does not know the unit will feel a hot tank, decide the tank is fine and run out of ideas.

If you want the water followed through the unit valve by valve rather than summarised, our explainer on how a Pulsacoil works does exactly that, and it is the fastest way to understand why the fault list below looks nothing like a cylinder fault list.

• Stored water heats the mains water through a plate, it never mixes with it
• No expansion vessel, no pressure relief valve, no tundish, no discharge pipe
• A pump and a control board sit between the heat and your tap
• Hot water is made at the moment you draw it, not stored ready to use
• Most are electric only, which is why they are common in flats with no gas

Which Pulsacoil you have and why it matters

Gledhill built several generations and they are not interchangeable. Knowing which one is in the cupboard decides whether a part is available, whether a board can be swapped and whether repair still makes sense at all.

The Pulsacoil 2000 and the Pulsacoil III are the ones we see most in London flats, typically fitted from the late nineties through to around 2010. Both use immersion heaters in the store, a pump and a plate heat exchanger, with a control board behind the front panel. The Pulsacoil A-Class came next and is the smarter unit, with a board that signals faults rather than simply going dead, and a different pump arrangement. Later still came the stainless models, badged Pulsacoil Stainless or PCS. Some variants took their heat from a boiler rather than immersion heaters alone, and Gledhill sold a closely related family under the BoilerMate name, which behaves in much the same way.

Age matters for a second reason. On the older boards the common failure is a relay or a dry solder joint on a board that is no longer made in its original form, so the fix is a current equivalent board plus the loom to suit, if one exists for your model. On the A-Class and later, parts availability is generally better. An engineer should be reading the model and serial plate before promising anything, not guessing from the shape of the case.

• Pulsacoil 2000 and Pulsacoil III, immersion fed, older style control board
• Pulsacoil A-Class, later board with fault signalling, different pump
• Pulsacoil Stainless and PCS, later stainless bodied units
• Boiler fed variants and the related Gledhill BoilerMate range

The data plate is usually on the front panel or inside the door. Photograph it before you call anyone. It saves a visit spent identifying the unit rather than fixing it.

No hot water from a Pulsacoil: what an engineer checks first

The first split is whether the store is hot. An engineer will feel the body of the unit high and low, or read the store temperature at the sensor, before touching anything else. A store that is cold top to bottom is a heating problem: the immersion heaters, their thermostats, the electrical supply or the board that switches them. A store that is hot but delivers cold water is a transfer problem: the pump, the flow sensing, the plate or the board output that runs the pump.

On the heating side, the two immersion heaters are checked for continuity and for insulation resistance to earth, and their thermostats are checked for a tripped overheat cut out. Most Pulsacoils run a lower element on the off peak supply to charge the store overnight and an upper element as a boost. If the off peak element or the off peak supply has failed, the classic symptom follows: nothing in the morning, but pressing the boost gives you a limited amount of hot water an hour later. That pattern points at the Economy 7 side, which can be the element itself, the contactor, the meter timing or a tripped breaker on a circuit nobody has looked at in years. The tests themselves are the same ones used on a conventional cylinder, so the symptom guide for an immersion heater not working applies here too, with the difference that the element is heating stored heating water rather than the water you wash in.

On the transfer side, the engineer opens a hot tap and listens. The pump should start within a second or two of the flow being sensed. Silence means the pump, its supply from the board, or the sensing that tells the board a tap is open. A pump that hums but does not shift water is usually seized, which is common on units that sit idle over a summer. A pump that runs correctly while the outlet stays lukewarm points at the plate heat exchanger.

Only after that does anyone start talking about the board. A control PCB is the most expensive single part in the unit and it gets blamed far too early. It should be condemned because its outputs have been measured and found dead, not because the unit is old and the symptom is confusing.

If an overheat thermostat has tripped, resetting it is a test, not a repair. If it trips again, something is letting the store run away, usually a failed control thermostat or a board sticking an element on, and continuing to reset it leaves very hot water in an open store.

The Pulsacoil faults that actually come up

Across the Pulsacoil range the same handful of failures account for most call outs. None of them are exotic. They are simply unfamiliar to anyone who has only worked on cylinders and combis.

Immersion heaters are first, and London water is the reason. Hard water scales an element until it overheats its own sheath and fails, or until the scale shell insulates it so well that the store takes far longer to charge than it used to. A slow charging store that still eventually gets hot is often an element half buried in scale rather than a control fault. Elements also fail to earth, which shows up as a breaker or RCD tripping when the off peak supply comes on in the small hours. The elements themselves behave exactly as they do in a cylinder, so the testing described on our immersion heater repair page applies here too, even though everything around them is different.

The pump is second. It is a small circulator doing a hard job, starting and stopping every time anyone runs a tap. Bearings wear, impellers stick after a period of no use, and in some cases the pump is fine but the board relay that feeds it has burnt its contacts.

The control PCB is third. Failures are usually partial rather than total: one output dead so the pump never runs, or a relay chattering, or the board reading a sensor wrongly and heating on the wrong schedule. Older boards suffer from heat cycling in a warm cupboard and dry joints follow.

Temperature sensing is fourth. A thermistor that drifts high makes the board think the store is charged when it is not, so you get a tank that never properly heats and an owner convinced the elements are dead. A thermistor that drifts low leaves elements running longer than they should. Sensors are cheap and are worth proving rather than assuming.

Fifth is the plate heat exchanger. This is where hard water does its quietest damage. The mains side of the plate scales up over years, the channels narrow, and the first thing you notice is that the shower is fine at half flow and disappointing at full flow. Eventually it is disappointing at any flow.

Last, and least welcome, is a leaking store. The tank body is the one part that cannot be repaired sensibly. Water appearing under the unit needs to be traced properly first, because a dripping float valve, a weeping pump head or a joint on the plate looks identical on the floor and is a far cheaper outcome.

• Immersion heater failed, scaled or leaking to earth
• Pump seized, worn or not being switched by the board
• Control PCB with a dead output, a burnt relay or dry joints
• Thermistor or store sensor reading wrongly
• Flow sensing not telling the board that a tap is open
• Plate heat exchanger scaled and restricting flow and temperature
• Feed cistern float valve passing and running to the vent or overflow

Pulsacoil hot water that starts warm and turns cold

This is the most reported Pulsacoil symptom and it almost always means the store is not holding the charge it should. The unit heats overnight, you get a bath and a shower out of it, and by the second shower it has gone. Because a thermal store gives up its heat through a plate, performance falls away as the store temperature drops rather than stopping cleanly like a cylinder emptying.

The most common cause is one element working and one not. With only the boost element live, the store heats the top portion only, which feels like success at the tap for a few minutes and then fades. The second cause is an off peak supply that is not arriving for the full period it used to, so the store starts the day part charged. The third is scale, either on the elements slowing the charge or on the plate limiting how much heat can cross per minute.

There is also a genuinely non fault version of this. A Pulsacoil sized for a one bedroom flat in 2004 is being asked to serve a rainfall shower and a bath in the same evening in 2026. The unit can be working perfectly and still not deliver that. An honest engineer will tell you when you have a sizing problem rather than selling you parts that will not change the outcome.

If you are not certain the Pulsacoil is the thing at fault, the general guide to water not getting hot is a useful sanity check first, because a scaled shower cartridge or a failed blending valve produces the same complaint from a unit that is working perfectly.

Why plumbers turn down Pulsacoil work

It is not snobbery. A Pulsacoil sits in the gap between two trades. The water side is plumbing, the control side is electrical, and the logic is specific to Gledhill rather than to any general principle a plumber already knows. A general plumber who opens the front panel finds a board, a loom, sensors and a pump, with no obvious equivalent to the cylinder thermostat and zone valve arrangement they were expecting.

On top of that, the products went out of production, so parts are model specific and not on a merchant shelf. Somebody who cannot identify the model cannot order the part, and a wasted second visit costs them more than the job pays. It is quicker for them to say no.

The practical consequence for you is that Pulsacoil owners get bounced. People describe calling three plumbers, having two decline on the phone and the third turn up, look at it and recommend ripping it out. Ripping it out is sometimes the right answer, but it should be a conclusion, not an opening position from someone who could not test the pump.

We keep Pulsacoil work in the rota deliberately, with engineers who have opened enough of them to know where the model plate lives and what a healthy store to plate temperature difference looks like. Our engineers are qualified for the work described here, and the electrical side of a Pulsacoil is treated as electrical work, not as a plumber poking at a board.

What you can check yourself before calling anyone

Some Pulsacoil call outs turn out to be a switch. It is worth ten minutes before you book a visit, and any engineer worth using will tell you the same.

Start at the consumer unit. Pulsacoils are often on two circuits, one permanent and one off peak, and the off peak one may be fed through a separate meter or contactor that lives in a cupboard or a communal riser. A tripped breaker on a circuit that only energises at night can go unnoticed for weeks. Check that the isolator or switched spur next to the unit is on, and that nobody has turned off a switch labelled water heater during decorating.

Then test the symptom properly. Run a bath tap rather than judging by the shower, because a scaled shower cartridge or a failing mixer produces the same complaint and has nothing to do with the Pulsacoil. Feel the body of the unit high and low, with care, and note whether it is hot, warm or stone cold. Open a hot tap and listen at the unit for the pump starting.

Finally look at the front panel for any lights or a display, and photograph what it is showing along with the model plate. Those four pieces of information, breaker states, store temperature by feel, whether the pump runs, and the model, are exactly what an engineer would spend the first twenty minutes establishing.

• Check both circuits at the consumer unit, including the off peak one
• Check the isolator or switched spur beside the unit
• Test at a bath tap, not at the shower
• Feel the unit top and bottom and note hot, warm or cold
• Listen for the pump when a hot tap is opened
• Photograph the model plate and any lights on the panel

Do not take the front panel off. There are live terminals behind it and stored water close to boiling. Everything in the list above is done with the panel closed.

Pulsacoil repair or Pulsacoil replacement

Repair is usually the right answer and it is usually the cheaper one. An element, a pump, a sensor or a board are all serviceable items in a unit whose tank is sound, and a Pulsacoil with a good store can carry on for years after a board change. Replacing a working tank because one component failed is a waste of a tank.

Replacement becomes the honest recommendation in three situations. The first is a leaking store, where there is no sensible repair. The second is a unit where the specific board or loom for that model can no longer be obtained, which is a real risk on the oldest units. The third is when the repair cost is stacking up across several failed parts at once on a unit that was already struggling to meet the demands of the household.

If you are replacing, there are three directions. Like for like, fitting a current thermal store into the same footprint, which keeps the plumbing and the electrics broadly as they are and suits flats where the cupboard is tight and there is no gas. A move to an unvented cylinder, which gives strong mains pressure hot water from a stored volume, but needs enough incoming mains flow and pressure to be worth it, a safe route for the discharge from the safety devices, and a qualified installer. Or a direct electric alternative sized to the flat. In a purpose built block there are also practical constraints that decide this as much as the technical merits: lift access for a new tank, whether the cupboard door will pass it, and whether the building has rules about what may be installed.

We survey before quoting a replacement, because the mains flow rate at the property is the fact that decides whether an unvented cylinder will feel better than what you have or worse. Guessing that from the doorstep is how people end up disappointed with a brand new installation. What the mains fed route involves is set out on our unvented cylinder installation page, and the wider decision between tank types is covered under hot water cylinder replacement.

Anyone recommending replacement without having tested the pump, the elements and the incoming mains flow is recommending it for their convenience. Ask what was measured.

Leaks, overflows and water where it should not be

Water running from a pipe outside the building, or filling a tundish style outlet, means something different on a Pulsacoil than on a pressurised cylinder. There is no pressure relief valve to blame. What there is, is a feed cistern in the top of the unit with a float valve, and a vent. If the float valve passes, the cistern overfills and runs to the overflow, which looks alarming but is a small part. If the store is overheating, it can push water over the vent, and that one matters, because it means a control has failed and the store is being heated when it should not be.

Water pooling under the unit itself needs the cause found before anything is ordered. A weeping pump head, a joint on the plate, a failed immersion heater gasket and a corroded store all put water in the same place. The difference between the cheapest of those and the most expensive is the whole job, so it is worth an engineer with a torch and some patience rather than a guess.

If water is actively escaping and you cannot see where from, turn off the electrical supply to the unit at the isolator and turn off the cold mains to the flat at the stopcock. That stops the two things that make it worse. It also stops the unit heating, so the store will cool, which is a fair trade while you wait.

If water is reaching a downstairs flat, treat it as urgent. Isolate the electrics and the mains, and tell the engineer on the phone that there is a property below affected so the visit is prioritised correctly.

Booking a Pulsacoil engineer in London

We cover London with twenty engineers, and Pulsacoil calls are routed to the ones who work on them regularly rather than to whoever is nearest. When you book, the two things that speed the job up most are the model from the data plate and a description of which half of the unit is failing, meaning whether the tank itself is getting hot.

A first visit is diagnostic and, where the part is a common one such as an immersion heater, a pump or a sensor, it is often also the repair. Boards and model specific parts are ordered against the plate details once the fault has been proved, which is another reason the photograph of the plate is worth taking before we arrive.

One point of difference is worth flagging on the boiler fed variants of these units, which take their heat from a boiler rather than from elements alone. There the pattern to test against is no hot water but the heating works, because the radiators warming normally while the taps stay cold moves the suspicion on to the diverter arrangement and the controls rather than on to the store. On an all electric unit that comparison does not exist, which is one of the reasons the model on the data plate decides the diagnosis.

The rate is fixed before we attend and the total depends on how long the job takes. Parts are separate and are confirmed with you before anything is ordered. If the honest conclusion is that the unit should be replaced rather than repaired, we will say so on the first visit and tell you what we measured to reach that view.

On how that is charged, a plumber call out fee is money for attendance rather than for a result, which is the part people find counterintuitive when a visit ends in a diagnosis rather than a repair. It is quoted before we travel and it does not change because the unit turned out to be awkward, and the rates themselves sit on the pricing page rather than in this copy.