(e.g. In this case, power needs to be isolated before testing. If theres a fault with the NTC thermistor you might find: Faults that cause a temperature differential on the flow, return, or both thermistors include: All work concerning gas, LPG and oil boilers should be completed by a professional, and not just for safety. If this limescale is deposited on the heat exchanged, it can spell trouble for the boiler. A scale reducer will help to prevent the high amounts of limescale in hard water from building up in the heating system. NOTE: If the water supply is the problem, ensure that this is rectified or this error will re-occur. Please dont hesitate tocontact usfor more info. If it is, replace the thermistor. They are used across a variey of industries, but play a vital role in delivering heat and hot water in your modern gas boiler, but what excatly is a thermistor? A limescale problem can build up within boilers over time. Mains water pressure problem or the mains water stop valve is closed. Old boilers should also be replaced with newer units, as modern boilers provide all the required safety features to prevent the dangers associated with overheating. When the limescale (which comes from mineral deposits in water) attaches itself to NTC thermistors, it can cause temperature sensing issues. 
Not only putting the boiler at risk of overheating but could also reduce the lifetime of the boiler. (Note that if this is a low probe wiring fault, the water will stop at the high level probe regardless of the status of the low level). You are using an out of date browser. If this limescale is deposited on the heat exchanged, it can spell trouble for the boiler. And has made no difference. What boiler is it and what is the boiler thermostat set to? It does not matter which lead goes to the terminals, as polarity is not important in this test. Lot's of how to's are on youtube. This indicates that the Thermistor is measuring zero resistance. Boiler Guide is operated by Leads.io Ltd. Fortunately, modern boilers are fitted with safety features that mean the unit will lockout before the boiler overheats. It will lock out and display a F72 fault code. 
The change in reading will not be smooth or there will not be any change. If you've noticed that any strange sounds from your central heating system then thats strong indications of a blockage. Low level probe has scale or mineral deposits on the low level probe metal tab preventing a reading of the water level. A qualified engineer will be able to assess the thermistor and decide whether or not it will need to be replaced. An overheating boiler can be a serious problem. Q: Why is the 'ready' status light flashing red? For a better experience, please enable JavaScript in your browser before proceeding. Check for kinks in hose and inlet valve is switched to open position. See instruction video. Since thermistors are designed to be temperature sensitive, testing them involves the application of heat. The thermistor probe is unplugged from the 4way connector on the PCB or the thermistor has failed open circuit. Damaged or faulty pumps can be fixed, so a faulty pump might not mean that a new boiler is required, but often pumps will need to be replaced to get the boiler working properly again. This will stop water running into the unit if any other safety measures fail, and itll reduce the risk of pressure building in the boiler. This website uses cookies to provide you with a better experience. google_ad_slot = "4618437032"; Leaks need to be found and fixed, before moving onto the issue at hand; the thermistors. I can confirm that the pump is definitely installed in the correct orientation. Unfortunately, these blockages can also result in an overheating boiler, and thats all the more likely if the blockages are significant. The PCB converts this into a temperature reading to know if water needs to be heated, or whether to switch the burner off due to water being up to temperature. By pressing Send youll agree to our privacy policy. To stop pressure rising so far that the unit explodes, the boiler will stop working. Find approved boiler engineers in your area. If your boiler stops working and overheating is suspected, make sure you turn off the water before you do anything else. A: Refer to the installation details of your specific model on individual product pages. It may not display this or other websites correctly. On my boiler at least, insufficient flow would result in kettling. A small Direct Current is sent to the thermistor via the potentiometer, and the PCB knows then whether to give more, or less gas to get the water to the correct temperature, depending on the small voltage drop due to the change in current. Speak to your engineer about whether a problem with the pump could be causing your boiler to overheat to find out what needs to be done to solve the issue. This will stop water running into the unit if any other safety measures fail, and itll reduce the risk of pressure building in the boiler. Calculations are based on a mid-range gas boiler and average installation costs depending Check thermal overload switch where fitted is pressed inward. Get in touch today! One of the main culprits to be aware of here is the pump, which circulates water around the system. The number one problem that causes damage to electrical components is water damage. Like all internal components in your boiler, the thermistors can degrade over time. Type of Business, e.g. If your looking for the list of error codes relating to the Vaillant boiler then please read the article Vaillant Boiler Fault Codes And Cures, EPHG LIMITED 2016 to 2022 All Rights Reserved. A boiler overheating can be a risky issue to fix, so unless you have the required skills and knowledge, its something thats best left to the experts. Typically, it will create a hotspot, so the temperature and resistance readings arent a true representation of overall water temperature. 
a bad earth (return) connection between the PCB and the Tank). Once youve turned off the water, its best to talk to an engineer about what might have caused the problem before trying to get the unit back up and running again. So, when looking for a heating engineer, make sure they're listed on the Gas Safe register. Above, weve mentioned that heat exchangers can leak. Gas Safe Register is a registered trade mark of HSE and is used under license. //-->. This error is only displayed after 20 mins of the heater being on continuously. The heat exchanger's role within the heating system is to heat cooler water before it's then circulated around the radiators. This checks that the water in the tank cools when the inlet solenoid valve is switched on. If your boiler begins to overheat then it will lockout. If within resistance range and wiring circuit is ok, replace main PCB 1600345 for Ecoboiler range. Trading address is B136 Riverside Business Centre, Haldane Place, London England, SW18 4UQ. We continue to follow safety and continuity measures across our commercial and operational functions globally, while protecting staff and recognising our social responsibility to minimise the spread of Covid-19. What else could cause a F72 fault code to be displayed? They are used in circuits and semiconductor applications. This checks that the water in the tank is cooled by when the inlet solenoid valve is opened. the probe is not in contact with the water. If the heating system has been making a lot of noise, or some radiators have been failing to heat up properly, its quite likely that theres a blockage in the system. electrical box on top) as the old, doesn't necessarily mean they are pumping the same way. Then when they arrive at your property remember to ask to see their Gas Safe ID. A: Refer to the spec sheets of your specific model on individual product pages. Condensing vs Non Condensing Boilers: Whats The Difference? Take a look at some of the most common causes to see which one your boiler might be affected by. Anthony Smith began writing for Demand Studios in May of 2009 and has since written over 1400 articles for them. How can a boiler engineer determine the correct resistance reading, if the NTC thermistors are faulty? There is a permanent temperature difference between the flow and return NTC thermistors, causing the F72 error to be displayed. google_ad_client = "ca-pub-8311241727691674"; Look for signs of a faulty thermistor. These temperature control sensors on a boiler dictate when the boiler fires up, and when it shuts down after getting to temperature. Some are 'wet' thermistors, whereby they are in contact with the water, some are 'dry' where they are attached onto a pipe and sense the heat transmitted onto the pipe. He attended the University of New Mexico, and has more than 25 years of experience in the business world. It assumes the thermistor has failed sort circuit. Thermistors are resistors that adjust to changes in temperature. Fortunately, this issue can be spotted before the boiler overheats. Heat the thermistor by moving your heated soldering iron tip to it. if a closed mains water stop valve is the problem, opening the valve will allow water into the machine and normal function will resume when the low level probe is reached), The water level is below the low level probe, which is normal when the machine fills for the first time. chronic air in radiators and concurrent boiler pressure rise - combi, boiler pump keeps turning off then back on, Gurgling noise coming from feed pipe to pump. google_ad_height = 15; (1 degree per minute), the inlet solenoid is switched off and the 6 flash cycle is displayed. So, take steps to clear these blockages by flushing the system before your boiler overheats and causes more serious problems. Taking these steps will help to keep your heating system running safely, reliably and efficiently. Thanks - Afraid I have lost a bit of faith in the professionals.. You must log in or register to reply here. This is a recoverable error. Fixing the issue that's resulting in the boiler overheating depends on the problem. Note the multimeter reading as you are applying this heat. The air pressure sensor gives a signal that pressures are within working range for the boiler to ignite, The pump receives a signal to begin circulating hot water, The boiler shuts off before getting radiators or hot water up to temperature, On the flip side, hot water burns hotter than it should, The boiler cycles on and off constantly, failing to get up to temperature, An incorrect resistance reading on the flow and return thermistors, A wiring issue between the NTC thermistor and the PCB, Thermistors that have been fitted to the incorrect pipes, Signals mean the fault code displayed, isnt the most relevant, Theres no fault code for the specific fault, and the closest fault code is a F72, Isolate the problem to limescale build-up, Dose the heating system with inhibitor (to break down limescale), Fit a scale reducer (a filter to catch limescale deposits), Reset the boiler to clear the F72 fault code. Usually when a boiler overheats, the unit will recognise that heat is rising to an unsafe level, triggering a safety feature which causes it to shut down. Simply take a few moments to pass through our simple online form and youll soon be contacted by up to 3 local heating engineers. See instructions below. Old heating systems sometimes suffer from blockages, which can occur anywhere in the heating system. google_ad_width = 468; And remember, boiler parts (such as the pump and fan) do vibrate. If there is a reasonable resistance (18-22) on the element it probably has not failed, so the wiring might be at fault or the PCB board has failed. /* GBFinlinelink */ Also, if your boiler was installed more than 10 years ago then you should seek a replacement as this will give you the opportunity to install a boiler with the latest safety features. When limescale has built up, the boiler will start to make a whistling noise due to the water being restricted. But, due to the internal heat of the boiler, condensation is created and this settles on these electrical components. Explaining Different Radiator Valves and Symbols. 11 The Point, Rockingham Rd, Market Harborough, LE16 7QU, Always use a Gas Safe registered engineer. All of the common causes that we've listed above will require a professional. If your boiler stops working and overheating is suspected, make sure you turn off the water before you do anything else. Although Vaillant states this as a possible cause, its highly unlikely. So, if you hear the sound of a kettle, contact a heating engineer who will be able to flush out the system and clear it of any limescale. They can be located in several places, but they are generally located on the flow and return pipes either in the lower part of the boiler, inside the combustion chamber, or attached on the heat exchanger outlet pipes. If pumping the wrong way you will need to: Thanks for previous advice. A properly functioning positive temperature coefficient thermistor will show a smooth and steady increase in the multimeter resistance reading. A thermistor gives a certain resistance reading at a certain temperature. A boiler overheating is often the result of the safety features failing. Theyll need to manually measure the temperature of the flow and return water/pipes. Check heating circuit wiring, all connections secure no burning. There are several reasons why a boiler might overheat, so it isnt always immediately obvious which problem has led to the overheating. Some thermistors readings are also used to tell the boiler whether to come on when the temperature gets too cold. A powerflush is a cleansing process that cleans the central heating system of all limescale, rust and various other bits of debris. Check water pressure. A: If water pressure is ok, descale is required to clean the probe assembly which detects the water level. Our highest priority at Marco is the health and well-being of our staff, our customers and our suppliers. Copyright (c) 2014 GasBoilerForums.com. Clean low level probe with scotch brite. Electricity and Magnetism: What Are They & Why Are They Important? If you're looking for boiler engineers in your area then you've come to the Is there anything else that can cause damage? Each will offer a free no-obligation quote for you to then compare. How will an engineer know if the NTC thermistors are fitted to the wrong pipes? If the boiler is overheating, that's what the error code will tell you. Some thermistors are also used to monitor an anti scale function, called a pump over-run facility, whereby the pump continues to operate until the temperature has decreased to a set temperature. If there is too much limescale on the heat exchanger, water flowing through it will be blocked, and the boiler then runs the risk of overheating. Time for a new boiler? i.e. Measures the rate that the temperature increases in a specified time. This can be due to old age, but typically its a build-up of limescale. This is a non-recoverable error. If water continues to run into the unit, it can turn into steam that rapidly increases boiler pressure, which then leads to an explosion. Should the thermistor fail then that could lead to the temperature of the water getting too high and result in the boiler overheating as a result. The fact that the new may be in the same orientation (e.g. There is no device on the boiler to determine which side the NTC thermistors are fitted. The F72 fault code is the first sign. The thermistor monitors the temperature of the water so that the PCB (printed circuit board) knows whether to increase or decrease the temperature depending on the demand. (Can be flashing for up to 2 min at start up), The low level probe wire is disconnected, or there is another wiring fault (eg. Whether you need help solving quadratic equations, inspiration for the upcoming science fair or the latest update on a major storm, Sciencing is here to help. Typically, you should expect to budget approximately: Depending on where you are in the country (and labour rates), expect the total cost of repair 150-200. What are the most common causes of a NTC thermistor temperature differential? They monitor temperature on the flow pipe (hot water leaving the boiler) and return pipe (water returning the boiler to be reheated). Another sign is if any of your radiators haven't been heating up properly. They are identical to look at as an NTC, they just behave differently. When the correct range of resistance is measured, normal operation resumes. Failing this replace PCB board 1600345 for Ecoboiler range. If this occurs, make sure you contact your engineer and talk to them about how to fix the limescale build-up before your boiler stops working completely. Short cycling can be a symptom of the boiler thermostat being set too low or defective. So, all it knows is the temperature readings are incorrect. You can see how this popup was set up in our step-by-step guide: https://wppopupmaker.com/guides/auto-opening-announcement-popups/, Your Country (required) A: From time to time Marco makes changes/ updates to the model range and releases Technical Bulletins. It occurs for a number of different reasons, ranging from limescale build-up and blockages to faults within the unit itself. Once youve turned off the water, its best to talk to an engineer about what might have caused the problem before trying to get the unit back up and running again. If a failed thermistor is to blame for your overheating boiler, then youll need to consult a heating engineer immediately. Radiators not heating up could also be a sign of excess air in the radiator, which can be released by bleeding the radiator. (Note: Temporary loss of water pressure can occur in certain sites particularly when various machines are plumbed to the same mains water supply.) Its getting this reading because the return thermistor has been fitted to the flow side (i.e. Therefore we can test across the components two connections with a multimeter set to read Ohms, and compare the reading we obtain against manufacturers charts at the current temperature. He also writes for "The College Baseball Newsletter." There are various parts that can leak in a boiler, but the most common are the: Some leaks are so small that you wont notice them. professionals. Heat the soldering iron. If it develops a fault then the hot water won't be able to leave the boiler which could cause the unit to overheat. If an overheating boiler isn't dealt with early on the unit becomes a risk to everyone in the property and the surrounding area. or if you are doing it yourself you can find suppliers local to you. The machine needs to be reset when this problem is solved. ---Coffee RoasterCoffee Shop OwnerEquipment Supplier/DistributorFacilities Management CompanyDesigner/SpecifierFoodservice/Hospitality ProfessionalCatering Company, Interested In (required) Boilers contain a thermistor, which is the piece of kit responsible for measuring the temperature of the water. If OK switch machine off and on again. What can cause an incorrect reading on NTC thermistors, and the F72 fault code to be displayed? on your requirement. ---Water BoilersCold Water DispensersCoffee Brewers. Get in touch with our team to find out more about overheating and how to prevent it. Q: What are the dimensions of my Marco product? This is a safety mechanism that has been introduced in recent years, and its something that all good modern boilers are fitted with. You could also have central heating inhibitor added to the heating system. If they can confirm the resistance reading is incorrect and this is limited to a thermistor fault, these will need to be replaced. If filter is fit bypass to check if filter is blocked. Thermistors work in conjunction with the user potetiometer (the boiler control knobs for temperature), and the Printed Circuit Board (PCB). In the event of a boiler overheating, components within the boiler could melt and release toxic smoke into the property. But, the specific measurement range is usually proprietary. Depending on your boiler, each thermistor will cost between 10-30. Learn about thermistors and how to check them with a meter. If the water supply is ok, reset the machine (switch the machine Off and On again). Begin your search by entering your postcode below. The process to clear the fault code is simple: This will help get rid of the limescale in the system, but also stop it from returning. 0% Finance Find the best boiler for your needs, or see how the latest A-rated boilers compare with each A limescale problem can build up within boilers over time. Q: I need installation details for my new Marco product. 1. When the correct range of resistance is measured, normal operation resumes. Limescale build-up on the heat exchanger can restrict the flow of water and lead to your boiler overheating. We only work with the best. If this continues for a period of time the boiler will inevitably start to overheat. An overheating boiler will usually mean a system shut down, but if it doesnt the situation can quickly become hazardous. A boiler engineer will be able to determine the correct reading on the flow and return thermistors, which will vary depending on the temperature the boiler is running at. Some modern condensers also have a thermistor checking for flue gas temperatures. The Vaillant fault code F72 boiler NTC thermistor problem Q & A or require an engineer for an emergency boiler repair. We recommend that boilers are serviced regularly. Over years, this can weaken or loosen wired connections. the machine does not need to be reset when the problem is solved. Each boiler (legally) must be tested. A boilers fault code system isnt full proof. Thats why its good to know how to recognise the signs of an overheating boiler. Luckily, these parts are not particularly expensive. If they malfunction, the circuit itself will likely malfunction, also. Select the supplier or trade you require, enter your location to begin your search. This leads to hot spots and the heat exchanger eventually cracking. In many cases, the main symptom of an overheating boiler is a shutdown. Thankfully, this is a rare occurrence these days, but an overheating boiler should still be attended to urgently to ensure that such a situation doesnt occur. A boiler overheating can be a risky issue to fix, so unless you have the required skills and knowledge, its something thats best left to the experts. In the past, a boiler overheating that wasnt fixed in time would have exploded, with potentially incredibly dangerous consequences. When it goes wrong, water temperature can rise to unacceptable levels, and that may well cause the entire unit to overheat. These are less common than NTC thermistors. Are you a trade or supplier? If the water pressure is within the specifications (5-50psi), the inlet solenoid should not be on for more than a few seconds. Replace thermistor connected to PCB. Normal when machine first fills. And a misdiagnosis could mean replacing the wrong parts, only to have the problem persist. 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