Guide hub
Boiler & Heating Pressure
A sealed system that will not hold pressure is losing water somewhere. What each fault code means, and how to find where it is going.
How to Repressurise a Boiler, and When Not To
The five-minute fix for a boiler on low pressure, and the one symptom that means topping it up is hiding a leak that is soaking your floor.
Vaillant F75: Pump Fault, or a Leak You Cannot See?
F75 means the pump started and the pressure did not move. Three things cause that, one of them is a leak, and this is how you tell which one you have.
Vaillant F22: Low Water Pressure, and What Took the Water
F22 is a safety shutdown at 0.5 bar. Topping up clears it in five minutes. How fast it comes back tells you whether you have a leak, and where to look.
Vaillant F28: An Ignition Fault, Not a Leak
F28 means the boiler tried to light and saw no flame. It is a gas, ignition or condensate fault, not a water leak. What it is, and who you should actually call.
Vaillant F29: The Flame Went Out, and Why That Is Not a Leak
F29 means the boiler lit and then lost the flame, and re-ignition failed. It is a gas or condensate fault, not a leak. What it is, and who to call instead.
Vaillant Boiler Losing Pressure: Finding Where It Goes
A sealed system should not lose water. How fast your Vaillant drops tells you whether it is the expansion vessel, the relief valve, or a leak under the floor.
Baxi E119 Fault Code: Low Pressure, or a Frozen Pipe?
E119 locks a Baxi or Potterton out before it fires. Baxi publishes E118 for low water pressure, so there are two checks to make and only one of them is a leak.
Baxi E133: A Gas Fault, Not a Leak
E133 on a Baxi or Potterton is a gas supply and ignition fault. Here is what you can safely check yourself, and why leak detection is the wrong call to make.
Glow-worm F22: Low Water Pressure, and Where It Went
F22 is Glow-worm’s low water pressure shutdown. Repressurising clears it; how soon it comes back tells you whether this is a leak or a sensor fault.
Glow-worm F1: An Ignition Fault, Not a Leak
F1 on a Glow-worm is an ignition fault, and Glow-worm links it to gas supply or a frozen condensate pipe. What to check, and why it is not a leak detection job.
Viessmann F2: An Overheat Lockout, Not a Pressure Code
F2 on a Viessmann means the temperature limiter has responded. Viessmann’s own first instruction is to check the fill level, which is where a leak comes in.
Which Boiler Fault Codes Actually Mean a Leak
A pressure code can mean the system is losing water. An ignition or overheat code does not. Baxi, Potterton, Glow-worm and Viessmann codes, sorted out.
How to Bleed a Radiator Properly
The right order, the right tool, and what to do when nothing comes out — plus the pattern that means the air is being pulled in through a leak.
What Should Boiler Pressure Be?
The cold reading, the hot reading, and what Worcester Bosch, Vaillant and Ideal each state, plus why a steady gauge beats a perfect number on it.
Boiler Pressure Too Low: What To Do
How to get the heating running again in five minutes, then how to work out whether the pressure fell because of bleeding, a vessel, or a leak.
How to Turn Off Your Water Supply
Close the inside stop valve clockwise, then drain the pipes at the kitchen tap. What that stops, what it does not, and what to do if it seizes.
Where Is My Stopcock?
Under the kitchen sink in most homes, and in the cellar head, airing cupboard or riser in London ones. How to find yours before you need it.
Ideal Boiler F1 Fault Code: Low Pressure, or a Leak?
F1 on an Ideal boiler means system water pressure is too low. How to clear it in five minutes, and how to tell an ordinary top-up from a hidden leak.
Ideal Logic L2 Fault Code: Why It Is Not a Water Leak
L2 on an Ideal Logic is flame loss or ignition lockout, not low pressure. What it means, the four checks Ideal ask for, and when to call a Gas Safe engineer.
Ideal Boiler Losing Pressure: Finding Where the Water Goes
An Ideal boiler that keeps dropping pressure is losing water from a sealed system. The overnight test that sizes the loss, and the four places it escapes.
Worcester Bosch EA Fault Code: Flame Not Detected
EA on a Worcester Bosch means flame not detected. The three checks Worcester list, why it is usually the condensate pipe, and when water is the real cause.
Worcester Bosch D5 Fault Code: A Condensate Pump Fault
D5 on a Worcester Bosch is a condensate pump fault. It is not heating water and not a pressure loss, but it can still put water on your floor or ceiling.
Worcester Bosch Losing Pressure: No Code, Just a Falling Gauge
Worcester say a heating system needs topping up once or twice a year. More often than that and water is escaping. How to repressurise, and how to find the loss.
Boiler Pressure Keeps Dropping: Leak, Vessel or Valve
Three different faults drop a boiler gauge and each needs a different repair. The cold-and-hot reading that tells a real leak from a vessel or valve fault.
Boiler Losing Pressure With No Visible Leak
Everything is dry and the gauge still falls. Where heating water actually goes when nothing is showing, and how the three causes are told apart properly.
Boiler Pressure Drops Overnight: What the Timing Means
A gauge that falls while the heating is off has ruled half the causes out for you. What an overnight drop points at, and the test that confirms it by morning.
Boiler Pressure Drops When the Heating Is On
Pressure that climbs while the heating runs and sits low afterwards is rarely a burst pipe. What the rise-then-fall pattern means and how to confirm it at home.
Expansion Vessel Failure or a Leak? How to Tell
A failed expansion vessel imitates a leak almost perfectly. The mechanism, the symptoms that separate the two, and why the wrong diagnosis costs you a floor.
Boiler Leaking From the Bottom: What Is Dripping
Water under a boiler comes from four different places and only two of them move the pressure gauge. How to identify which before an engineer opens the case.
Pressure relief valve passing water
A relief valve that weeps is usually obeying the system, not failing it. How to tell an over-pressurising system from a valve fouled by debris.
Tundish dripping: what the water is telling you
Water in the tundish is not a leak. It is a safety valve discharging where you were meant to see it. What a drip means, what a flow means, and what never to do.
Water pressure vs flow rate: which one you actually have
Pressure and flow rate are not the same thing, and mixing them up is why people buy pumps they are not allowed to fit. How to measure flow with a jug.
Why a system loses pressure overnight, and how to test it
Overnight is the cleanest measurement you can take on a water system. How to run the standing test properly, and what a measured loss actually rules out.
Central heating leaks: how to narrow down where the water is going
A sealed heating system should not lose water. Three checks that tell you which part is leaking — valve, radiator, vessel, buried pipe or boiler.
Vaillant F23 fault code: temperature difference, circulation or a leak?
Understand Vaillant F23, record the right symptoms and distinguish a circulation fault from pressure loss before paying for boiler repair or leak detection.
Vaillant F24 fault code: rapid temperature rise and circulation
Understand Vaillant F24, record when the shutdown happens and separate low pressure from circulation faults before paying for parts or a hidden-leak search.
Vaillant F27 fault code: flame detection, safe action and repair questions
Understand Vaillant F27, collect useful evidence and arrange the right engineer. Learn why the code does not prove a failed PCB, low pressure or a hidden leak.
Vaillant F20 fault code: temperature shutdown and what to do next
Vaillant F20 explained using specific manufacturer manuals. Understand the shutdown, record useful symptoms and separate boiler repair from a heating-water leak.
Ideal F2 fault code: flame loss, supply checks and the right repair route
Understand the Ideal F2 fault, model-specific flame-loss guidance and useful supply observations. Learn when to call a boiler engineer and why topping up is different.
Ideal L1 fault code: overheating, circulation and repeat lockouts
Understand Ideal L1 using manufacturer guidance. Record pressure and heating symptoms, avoid unnecessary pump replacement and identify when water-leak work is relevant.
Ideal F3 fault code: fan fault, repair evidence and safe next steps
Ideal F3 explained with manufacturer references. Learn what to record, why the fan is not automatically the failed part and how to assess a proposed repair.
Baxi E110 fault code: overheat lockout, model checks and next steps
Understand Baxi E110, confirm the correct boiler generation and record useful overheat evidence. Learn why a reset or pressure top-up may not resolve the cause.
Baxi E125 fault code: circulation problems and what to check next
Baxi E125 circulation fault explained with manufacturer sources. Separate water pressure from circulation, prepare an engineer visit and avoid speculative leak searches.
Baxi E118 fault code: low pressure, filling instructions and repeat losses
Understand Baxi E118, find the right filling guidance and record recurring pressure loss. Learn why the fault threshold is not a filling target or proof of a hidden leak.
Boiler Pressure Too High? How to Reduce It Safely
How to bring a high boiler pressure back to 1 to 1.5 bar yourself, why it went up in the first place, and the rising-pressure faults that need an engineer.
Radiator Not Heating Up? The Causes, in Order
One radiator cold or all of them lukewarm when the heating comes back on in autumn: the checks to make yourself, in order, and the pattern that means water is leaving the system.
If you need the repair
Other guide hubs
Thames Water
The letter, the four-week window, the allowance, and exactly where Thames Water’s pipe stops being their problem and starts being your repair bill.
Water Bills & Meters
Reading the meter to prove a leak, what an unexplained jump actually costs you per day, and the evidence a water company wants before it grants an allowance.
Insurance Claims & Trace and Access
Written from the engineer’s side: what the loss adjuster asks for, what a trace report must contain, and what gets a claim declined.
Field Notes
What we actually find on London leaks, what the law and the insurers changed this year, and the jobs worth writing up.
Hot Water, Cylinders & Tanks
Cylinders, storage tanks and the discharge pipes that give them away. Written from the leak end: what is losing water, where it is going, and what it costs to put right.