(Solved) Bosch Greenstar Combi 151 Problems

To help you understand the common Bosch Greenstar Combi 151 problems this article discusses 5 of the most common issues with their solutions.

The Bosch Greenstar Combi 151 is one of the best boilers to get on today’s market. And it’s crucial to understand the common problems that Bosch Greenstar Combi can have if you have one of these boilers in your home.

Although not all boiler malfunctions necessitate the assistance of a professional, knowing the common issues and problems that may occur will save both your time and money. It might even save your boiler from further malfunctioning.

Common Bosch Greenstar Combi 151 Problems And Reasons

No.Probable problemsEasy solution
 1Leak in the BoilerConsult with Gas Safe Engineer
 2Low pressure of the boiler                Find out the failed joints and seal it
 3Unusual noise in the boilerStop overheating the water
 4Stop heating waterIncrease the pressure gauge
 5Condensate pipe frizzingThawing out and insulating contents of the pipe
 6No power supply on the heaterReplace PCB (circuit board)
 7Faults in radiatorUse a chemical flush to reduce sludge, dirt
 8Stop responding to the thermostat.Replace the battery
 9The pilot light keeps turning off.  Take the help from an expert or clean the carbon deposits
 10Not no hot water in the boiler.                Turn on the central heating switch

Problem 1: No Heating Or Hot Water

If your boiler stops doing what it was supposed to do, providing your home with warmth and heated water, it can get quite frustrating. What you need to do to solve this is to determine the cause and then solve it.

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  • If this problem is occurring because of low pressure, then you have to examine whether the pressure goes below or not. If it is, it will need to be repressurized.
  • If a malfunction in the boiler’s thermostat is causing erratic heating or hot water, you should check the boiler’s manufacturer’s documentation for a potential fix; if you don’t find any issue, contact the manufacturer for assistance.
  • We recommend contacting a certified engineer if these solutions don’t work since issues like a damaged motorized valve or a malfunctioning diaphragm would necessitate professional assistance.

Problem 2: A Faulty Pilot Light

This also happens due to various problems. You need to examine whether the issue can be solved by yourself or whether you need a professional.


  • If you’re confident in changing this light, you might try to relight the pilot light on your own. But while doing that, you need to go through the boiler’s handbook for specific instructions.
  • Before you begin, make sure the gas stopper is turned on. Also, check if the supply of gas is proper. You can double-check this by examining your other gas appliances.
  • If you see a problem in the gas supply, to resolve this problem, it is best to consult a Gas Safe certified engineer.

Problem 3: Leaking Boiler

If the leak is occurring through the pressure valve, the boiler system’s pressure is probably too high. If the leakage is due to a malfunctioning of the pump seal, the seal may have worn out. But corrosion is to blame for a leak that has occurred around the boiler system’s pipes. So there can be various solutions.


  • If the issue is corrosion, there might be a problem with the installation of the boiler. We recommend you seekingan aid of a skilled one who can help you find and resolve this problem.
  • Almost all leak issues will need an engineer. The engineer might suggest that you get a new boiler set up if, somehow, the leak is caused by a severe malfunction.
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Problem 4: Low Boiler Pressure

By looking at the installed pressure sensor on the boiler, you can generally tell if the pressure is below the average point. You can usually fix the pressure at 1.5 bar. If it was less than one, your boiler would not work correctly.


You can start by looking for visual indicators of a leak, but you must not dismantle any casing. We recommend contacting an engineer if you notice a leak. If you can’t find a leak, you can repressurize the boiler if you’re confident in doing so. What you need to do is:

  • Allow the boiler to fully cool before turning it off.
  • Find the boiler’s key and fit it in the hidden tray just below the boiler.
  • Then, ensure the key is aligned with the given “open padlock” indication before inserting it inside the groove.
  • Then, as the key is now firmly inserted, flip it to the “closed padlock” indication.
  • You should now be able to hear the water flowing in the boiler when you twist the square (white-colored) nut clockwise.
  • Continue doing so until the pressure reaches 1.5 bars.
  • Next, when the water stops flowing, rotate the same nut clockwise.
  • Return the key to the indication that says “open padlock.” Some water may leak out, but this isn’t a problem.
  • Then re-start the boiler system.

Problem 5: Boiler Noises

It’s typical for a boiler to make little noise while it’s running, particularly when it’s first starting up. But, if a boiler starts making strange gurgling, pounding, or whistling noises, it needs to be repaired.


Depending on the sound, you can try the following steps:

  • Due to trapped air in the system, you can hear a gurgling noise, which will require bleeding of the radiator to release the air.
  • A gurgling noise indicates your boiler has low pressure; just work on increasing pressure.
  • Too much heating can create a banging noise, which will need to cool down the boiler.
  • In times of kettling, you will need an engineer to fix your boiler noise.
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This Video Will Help You Too!

Frequently Asked Questions (FAQs)

Why is my combi boiler not giving me hot water?

The reason behind your combi boiler not giving you hot water could be your boiler’s thermostat failure, leakage, failure in gas or electric source, or inadequate cylinder size.

How do I reset my Bosch combi boiler?

Follow the instructions in the manual for resetting your device. To reset a Bosch combi boiler, hold down the reset button for approximately two to three seconds. This will stop that reset button as well as the boiler’s fault indicator light from flashing.

Where is the reset button on the Worcester boiler?

The location of the reset button on the Worcester boiler varies from model to model. Go through the manual book that comes with your boiler to know the exact location of the reset button.


Knowing the Bosch Greenstar Combi 151 problems will help you identify the problems before your boiler malfunctions even more.

When the problems are small, Fixing them can save a lot of money and give your boiler longevity. So the next time you see any of these problems, don’t delay. Immediately identify the issue, fix what you can, or call an expert to help you fix your Bosch Greenstar 151 problems.

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