Potterton Boiler Repair, London

What the boiler is saying: system pressure has fallen below roughly 0.5 bar, too little to fire safely. It is the most common Potterton code by a wide margin.

The part almost nobody is told: pressing reset does nothing for an E119. The code will not clear until the water is back, and people press reset a dozen times convincing themselves the boiler is dead when it is simply waiting to be filled.

What you can safely do: find the filling loop, usually a braided silver hose under the boiler, and open it until the gauge reads between 1 and 1.5 bar cold. Close it fully. The code clears itself.

• Once or twice a year: normal. Sealed systems lose a little water.
• Every few weeks: a leak, often a radiator valve or a pinhole under a floor.
• Every few days: the expansion vessel has lost its air charge.

The exception: a healthy 1.2 bar on the gauge with E119 still showing means the pressure sensor has failed rather than the pressure.

The boiler called for gas, tried to ignite, saw no flame and shut the valve. Second most common on a Promax, and it has three usual causes in a reliable order.

First, the gas. Does the hob light? Has a prepayment meter run out of credit? An E133 with no gas anywhere in the property is not a boiler fault at all.

Second, in cold weather, the condensate. The white plastic pipe running outside to a drain freezes and the boiler cannot discharge, so it stops. Pour warm water along it, never boiling, which splits it.

Third, the electrodes. Worn or cracked, so the spark earths out before it reaches the burner, or the flame is never confirmed.

The part that gets blamed wrongly: the control board. Shutting the gas off was the board doing its job.

One reset only. Repeated attempts wear the ignition electrode faster and change nothing else.

The water went past the limit the safety thermostat allows and the burner shut down.

In practice it is: a jammed pump or air in the circuit, so the boiler is making heat faster than the system carries it away and it cooks in one spot.

The part that gets blamed wrongly: the safety thermostat, which is the part reporting the problem. Replace that and leave the circulation alone and it trips again within days.

When it appears after somebody has worked on the heating, air is almost always the answer. Refilling a system introduces it and air is exactly what stops water carrying heat away. Say so when you call, because it points straight at the cause.

What helps most: getting the sludge and air out of the pipework rather than replacing a component.

The boiler is firing but water is not moving through it properly. Close relation of E110, and the two often alternate on the same boiler across a few weeks.

In practice it is: a pump running without shifting anything, a valve seized shut, or a heat exchanger silted enough to restrict the flow through it.

Worth checking yourself: are all the radiator valves genuinely open? A thermostatic valve that has seized closed over the summer is a common cause and costs nothing to find.

In a flat: this code turns up disproportionately where the system has never been flushed since installation, which on a rented property is more often than not.

The board asked the fan for a speed and did not get it back. E161 is the same family.

Check the connection before the fan: on this range a plug that has worked loose at the fan produces an identical code to a failed fan, and that is a very different bill. Any engineer should look there first.

The warning you probably had: a worn fan bearing gets loud weeks before it stops. If the boiler has been noisy, that was this.

The part that gets blamed wrongly: only the fan. A flue blocked by leaves or nesting material makes a healthy fan work against resistance the board reads as a fault.

The catch-all. It covers a genuine control board lockout, but it also appears while the boiler is restarting after the electricity has been interrupted.

What to do first: reset once. If the power flickered, a breaker tripped, or somebody has been working on the consumer unit, an E168 that clears on one reset and never returns was the power cut rather than the boiler.

What it usually is if it comes straight back: the control board, and at that point the age of the boiler starts to matter more than the fault does.

The part that gets blamed wrongly: a reason to keep resetting. One attempt tells you what four would.

If your Potterton has no digital display and simply shows a red indicator, you have a Suprima or one of its contemporaries, and none of the E codes above apply to it.

What the light means: a lockout, and that is all it tells you on its own. Unlike a numbered code it does not name the fault, so the diagnosis has to be done at the boiler rather than over the phone.

What is worth noting before anybody attends: whether the light is steady or flashing, whether anything else on the panel is lit, and what the boiler was doing when it stopped. Was it trying to light, or had it been running?

The honest position on these: a Suprima is old enough that the answer often turns on whether the part is still made rather than what has failed. We will tell you that before you pay for a diagnosis rather than after.

Potterton, Baxi and Main are all Baxi Heating. They are not competing manufacturers, they are one company selling into different parts of the market, and they share fault codes and a great many components.

Why this matters more than it sounds: parts availability is far deeper than a single badge would suggest. A component that looks discontinued under the Potterton name is often still made and stocked under another, which can be the whole difference between repairing a sound boiler and replacing it.

Where it catches people out: a quote for a genuine Potterton part can be met with a much cheaper equivalent carrying a different brand name, and both are correct. Ask which group a part comes from rather than which name is printed on it.

We repair Baxi and Main alongside Potterton for exactly this reason.

Potterton made floor standing boilers in large numbers, and plenty of London houses still have one sitting in a kitchen or a utility room rather than hanging on a wall.

What you need to know: these are almost always heat only boilers feeding a hot water cylinder, so a hot water problem may not be the boiler at all. The diagnosis covers the appliance, the cylinder and the controls between them.

What changes if you replace it: swapping a floor standing boiler for a modern wall hung one frees a substantial amount of floor space, which in a London kitchen is worth something in itself. It also usually means new pipework, a new flue route and sometimes a new gas supply, and any quote should say so from the start.

Tell us when you call: say it stands on the floor. It changes what an engineer expects to find and how long we allow.

The Promax was fitted in very large numbers into flats and rented houses, and a system that has changed hands several times has usually never had anything done to it beyond an annual gas safety check.

What that produces: magnetite settling where flow is slowest, so radiators go cold at the bottom or at the far end of the run, the pump works harder than it should, and eventually E110 or E125 arrives.

Why it is worth knowing: at that point the boiler gets blamed for a problem that lives in the pipework, and replacing the appliance without dealing with the system means the new one inherits the same conditions.

What to look for: radiators cold at the bottom while warm at the top, or a system that takes a very long time to come up to temperature. Both point at the water rather than the boiler. Our page on system flushing covers what is involved.

No code, no lockout, and one half of the system simply not working. On a Promax combi this is the diverter valve, and on a system boiler with a cylinder it is the motorised valve out on the pipework.

Why it matters which: they look identical from the outside but they are in different places and cost different amounts. If your house has a hot water cylinder in a cupboard, the part is probably not inside the boiler at all.

What to tell us: whether the boiler fires at all when you run a hot tap, and whether there is a cylinder anywhere in the property. Those two answers usually settle it before an engineer sets off.

Does the boiler fire when you run a hot tap? Call 0203 868 6134.

Potterton name the range, then the type, then the output. A Promax Combi 28 HE is a Promax range combi rated 28 kilowatts.

• Combi: no cylinder, hot water made as it passes through.
• System: built to run a separate cylinder, with the pump and expansion inside the boiler.
• Heat or Regular: a cylinder in the airing cupboard, usually with a tank in the loft.
• Store: a combi with a small internal hot water store, which behaves like neither.

Anything other than Combi means there is stored hot water somewhere in the house, and the cylinder is as likely to be the fault as the boiler is.

Promax is the one you see most in London, particularly in flats and rented property. Digital display, E codes, parts widely available.

Titanium, Gold and Assure are the more recent ranges and use the same code system.

Suprima is the generation before that. No digital display, a red indicator light, and old enough that availability rather than cost usually decides a repair.

Netaheat, Profile, Performa and Puma are older still, and include floor standing models. Some are genuinely at the end of the line for parts and we will say so rather than take a diagnosis fee to tell you afterwards.

Potterton guarantees run for different terms by range, and the term is often longer than people assume, so it is worth checking before you spend anything.

The condition that catches everybody: registration. The boiler generally has to be registered within a set window after installation, and it has to have been serviced every year since. Miss either and the cover can be void even though the term has not expired.

What to look for: the Benchmark checklist in the back of the manual, filled in and stamped at installation and at each service. If it is blank, that is worth knowing before you make a claim rather than during one.

You need the serial number from the label. If you are still covered, the manufacturer's engineer is the cheaper call and we will tell you so.

The cylinder sensor is a small part in a pocket on the tank, and when it fails the boiler simply stops heating your stored water while the heating carries on faultlessly. Inexpensive, quick, and invisible to anybody looking only at the boiler.

The motorised valve routes heat to the radiators or the cylinder. A failed motor or microswitch produces heating without hot water, or the reverse, or both running when you asked for one. The head normally changes without draining the system.

The immersion element scales until it trips or stops. It is worth testing rather than assuming, because an element costs far less than a tank. Across the larger properties in Notting Hill and Holland Park a scale reducer usually goes in at the same time.

Because an unvented cylinder holds mains pressure, it carries a set of safety devices: an expansion vessel, a pressure reducing valve, an expansion relief valve and a temperature and pressure relief valve, all discharging through a tundish. Water at the tundish is the system reporting that one has failed, and capping it is never the answer.

That work is notifiable and requires G3 as well as Gas Safe registration. We hold both, so the appliance and the cylinder are diagnosed on the same visit rather than across two. It is why our unvented cylinder repair is not farmed out to somebody else.

Removing a cylinder to reclaim an airing cupboard is the decision we are asked to undo more than any other. However large the output figure, a combi heats water as it passes rather than storing it, so it cannot serve two showers at once. With three bathrooms the right answer is almost always to keep stored hot water, and to replace an ageing cylinder rather than lose it.

At this age the parts are current and the fault is a component, not the appliance giving up. A sensor, electrode, fan or pump on a six year old Promax is a repair, without qualification.

Check the guarantee first, including with us, and check the registration and service history as well as the term. Both conditions matter and people usually only think about the years.

Quoted for a replacement at this age? Ask which one part failed, and what that part costs by itself. The gap between those two answers is usually the whole conversation.

Still a clear repair: electrodes, pressure sensor, fan, pump, expansion vessel, diverter valve. Ordinary wear items that say nothing about the condition of the rest of the boiler.

The conversation changes with a main heat exchanger, or a second significant failure inside a year. At that point the arithmetic favours replacing the boiler, and the question is what goes in the next two winters as much as what has gone today.

Potterton's advantage here is the shared parts bin. Because Baxi and Main use many of the same components, the supply chain is deeper than the name on the front suggests and fewer repairs stall waiting for something to arrive.

Past this point availability takes over from cost. A Suprima, Netaheat or Profile can be mechanically sound and still unrepairable because the one part it needs is no longer made, and a repair then is not slow or expensive, it is impossible.

A floor standing boiler adds a second consideration, because replacing one is a larger job than swapping a wall hung appliance. New pipework, a new flue route and sometimes a new gas run, and the figure should reflect that from the first quote.

Before you spend anything on a diagnosis, we will find out whether the part can still be had. There is more on what drives the price in our guide to repair and replacement costs.