Bosch Greenstar Combi 151 Problems [5 Easy Fixes]

The most common Bosch Greenstar combi 151 problems are that the boiler is not heating, it’s leaking water, losing pressure, making banging noises, and leaking gas.

Keep reading this Bosch Greenstar Combi 151 troubleshooting guide to learn more about these problems and how you can fix them. Let’s jump in!

Table Of Contents

Bosch Greenstar Combi 151 Problems [5 Easy Fixes]

In this section, we will explore the most common Bosch combi boiler problems and how you can fix them.

1. Bosch Greenstar Boiler Not Heating

Many factors can contribute to the Bosch boiler not producing enough heat to keep your room warm. These are:

  • The radiator valves of the thermostat are set too low.
  • Low temperature set to the central heating flow of the appliance.
  • The temperature is set too low on the room thermostat.
  • The heating system has trapped air.
  • The pressure of the water system is low.


You can fix the Greenstar boiler not heating issue by following these steps:

  • Increase the temperature of the thermostatic radiator valves.
  • Rise the temperature of the central heating flow.
  • The temperature of the room thermostat has to be set to a higher temperature.
  • Drain the radiators and the heating system needs to be reset.
  • Reset the pressure of the water system.

2. Bosch Greenstar Boiler Leaking Water

Bosch combi boilers start to leak water if you’ve been using them for a while. The tubes or blocks which pass the water are made of plastic.

The plastic becomes vaporized and melts. That causes the water to leak through the melted or broken plastic.


The plastic block that is causing the problem has to be replaced. It’s best to consult a Gas Safe registered engineer to do this job as the boiler needs to be opened and accessed.

Hiring these engineers are expensive but safety is more important than saving money here. You will be opening up yourself to unnecessary risks if you decide to do it on your own.

3. Bosch Greenstar Boiler Losing Pressure

Water leakage causes the boiler to lose pressure. But water leakage can happen in different areas. The leaks commonly happen at the Pressure Relief Valves, heat exchangers, or radiator pipes.

The water gets into the combustion chamber when it leaks from the heat exchanger. You won’t be able to hear it since this water goes to the drain. But the boiler could lose pressure because of it.

The PRV valve can also be leaking. You can easily check for a leaking PRV valve and see if it’s wet and damp. If it is, then it’s leaking.


Take off the cap above the radiator pipe and see if that’s been leaking before you check your boiler. Tighten the nuts and bolts of the radiator to stop the leak. If the issue is solved, it was the radiator that was causing the problem.

If there’s no sign of a leak from the radiator, the issue may be with your heat exchanger or the PRV valve. You’ll have to call in a technician if it’s the heat exchanger that’s leaking.

4. Bosch Greenstar Boiler Making Banging Noises

The banging noises in a Bosch Greenstar boiler can be caused by a faulty thermostat or a drop in the water pressure. It can also be caused by kettling or the build-up of limescale. 


If you hear banging noises, you should start working immediately to fix the issue. It’s best to call in an expert as the drop in water pressure is caused when air gets into the heating system.

The boiler needs to be taken apart to fix this issue. This job is done best when it’s handed to someone who knows what he’s doing.

5. Bosch Greenstar Boiler Leaking Gas

The most common reason behind a boiler leaking gas is a faulty gas valve. You’ll be able to tell if this is happening as there will be the smell of gas around the boiler.


You must open up all the doors and windows and let the gas go away. If there’s a gas leak and it comes into contact with flame, it can lead to a massive accident. So, bring in a technician quickly to fix this issue.

There’s also a chance that it will smell like a gas leak even when that isn’t the case. Sometimes the smell can come from the boiler burning dust that has accumulated with the usage or overheating of the boiler.

However, consulting a technician is the best course of action since you can’t be sure what’s causing the problem.

Bosch Greenstar Combi 151 Specs

Here are the specifications of the Bosch Greenstar Combi 151 boiler:

  • 151.6 MBH Input Maximum.
  • 96.8% Efficiency.
  • 3.17 Gallon Expansion Tank.
  • 4.0 GPM Flow Max


How to reset the Bosch Greenstar Combi 151 boiler?

Pressing the reset button for two to three seconds will reset the boiler. The boiler will restart and go back to the default settings if the programmer and thermostat are okay.

What does the Eco Button do in Bosch Greenstar Combi 151 boiler?

The boiler normally preheats and stores hot water for you to minimize the delay when you use them. But when you turn on the economy mode, it will no longer preheat and store the water.

That means that you’ll save money in the long run by turning on the eco mode. But you’ll have to wait a little longer before the hot water starts pouring in. It’s a trade-off between comfort and saving money.

Why should you choose a Combi boiler over a traditional boiler?

Combi boilers are usually better than traditional boilers since they’re more efficient. The water also heats up directly from the mainline. The waiting time is also less for combination boilers compared to traditional boilers.

Why is my Bosch Combi boiler light flashing?

If there is blue fashing light, it indicates gas supply issues. There is also a light that shows when the boiler is in service. It’s best to call a technician if any of these lights are flashing.


Now you know the most common Bosch Greenstar Combi 151 problems and how you can solve them. If you need to open up the boiler to fix any issues, consult someone who is Gas Safe Registered.

We hope this article has helped you understand where to look if you’re facing any of the common problems of Bosch boilers. Drop a comment below if you have any questions.

Note: You can also read how to fix Mr heater big maxx problems.

2 thoughts on “Bosch Greenstar Combi 151 Problems [5 Easy Fixes]”

  1. Hello,
    I have a Bosch Combi Boiler installed appox. 2 years ago and is making a sound of A jet then a bang threw the heat registers. The technicians have been out at least 6 or 7 times trying to get air out of the system but the problem still exist. Could there be a problem that they are missing, the techs have replaced the expansion tank and the Spiro vent and also drained the boiler many times. The boiler does maintain the pressure and it seems to be in just one zone. Thank You Bill Mackie

    • Hi Bill

      Your Bosch Greenstar boiler produces such sound may be due to a faulty thermostat or a drop in the water pressure. It can also be caused by kettling or the build-up of limescale.

      Well, to fix the issue, it would be wise to contact the Bosch Greenstar customer support center or your local Bosch dealer.

      Best of luck!


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