Boilers FAQ


Thinking about calling us? Great. But before you do, you might find what you are looking for here. This is a list of the most common questions that we receive. Take a look, and if your question isn’t there then we would be our pleasure to answer it over the phone.


What’s included in our boiler service?

As with most things, the best answer can be found in a book.
If you flip your manufacturer’s instruction book to one of the last pages you will find a step by step guide to what’s involved in a boiler service.
Though that is your best reference, here is a  quick breakdown of what we do 
Tightness test
Working pressure
Condition of the parts and seals
Striping and cleaning the burner
Combustion analysis
Cleaning of condense trap
Checking condition of the flue and fan
Empty the magnaclean filter (if there is one)

Put simply, our service is sure to include everything possible to safeguard your boiler from failing in the future.

Is there is a difference between a boiler service and a boiler repair?

Definitely. If your boiler stops working for any reason – that then becomes a boiler repair job and you can expect a few parts to be replaced. With a boiler service the name of the game is preventing exactly that. It’s about increasing lifespan. For example, if your boiler is noisy because of an incorrect mixture of air and gas then a service will solve the problem, but when the appliance is full of gunk and the heat exchanger has failed then it’s time to repair.

Do we give estimates for boiler repairs?

Mostly, no. The main reason for is because in many cases finding the problem takes more time than the repair itself (strange, but true). When we do search for the fault on your boiler we want to make a 100% sure that we are correct before we begin the work (boiler parts can be expensive!). This keeps costs down for you and makes the job a joy for us.

What’s the difference between a safety check and a boiler service?

A safety check involves checking all relevant appliances in your home for safety. However, this does not involve any attempts to repair or improve these appliances. With our boiler service, we tend to polish things up for you (such as changing seals, replacing washers, general cleaning and so on).

How can I check if the engineer is registered with Gas Safe?

It’s very simple: insert his gas safe number into the gas safe website (make sure you choose the right option – business or individual), and after that you will probably see the picture of the engineer, however sometimes it’s simply a full name and accreditation.

Do I need someone qualified to replace my unvented hot water cylinder?

Absolutely. The unvented cylinders may be quite dangerous when wrongly installed. Don’t take our word for it, check this video out by Myth Busters:
Don’t worry, each of our technicians has the necessary qualification to install unvented hot water cylinders. Stay safe and book with us.

Do I need inspection hatches if a flue from my boiler is running in voids, ceilings or walls?

Yes. According to new regulations, a gas engineer has to have a visual on every flue connection to make sure it has been properly installed. This is to eliminate the chances of a possible flue carbon monoxide leak.

Replacing my boiler; what should I check?

When you decided to replace your boiler from an open vent system boiler to a combination boiler there are a few factors that have to be checked prior to installation.
1. Mains water pressure has to be above 1bar.
2. Dynamic flow rate min 9 liters per minutes on the highest draw-off point in property.
3. Gas pipe must be 22mm or higher instead of 15mm ( this was the most common gas pipe size in the olden days), in this case if the size of the pipe doesn’t meet the criteria then we will run another line starting from the gas meter all the way down to the boiler to supply enough gas to the new appliance.
4. Flue termination. All clearances must be established. Most of the time this means a minimum of 300mm from any openable window or door (Valliant) but every manufacture may specify according to their requirements.

These are the main factors when it comes to a decision. However if your property doesn’t have enough pressure and the flow rate is poor it may be overcome by using mains water boosting pumps. It’s not the cheapest way to increase the pressure but is definitely worth considering.

5. Termination of the condense pipe. It is always best practice is to terminate inside the property to protect it from outside conditions which could freeze the pipe. When that’s not possible and the only option is outside termination – adequate insulation has to be used to minimize the chances of freezing.

Before changing the gravity system to fully pressurize you have to be fully aware of potential leaks caused by conversion  (perhaps because your existing system is old or  the work done on it years ago wasn’t  top notch). Instead of existing on 0.4bar,  you will have up to 2bars  or higher in certain circumstances, so it’s much higher than what it was before. This means more stress on the pip joints and connection. Speaking from our own experience it’s very rare. But, from statistics it does happen about twice on every hundred installations.  These repairs are not included in the boiler replacement quote as they are unforeseeable circumstances. But rest assured, if it’s a simple job we will do it free of charge (up to about 30 minutes of extra work). 

Replacing a combination boiler?

In most cases, this is a straight forward job but there are a few factors to be taken into consideration:
1. Size of the previous boiler Roughly speaking, best practice is to use a similar size to the old one. However, this isn’t always true as mains water pipes have been changed in many London areas, allowing more water to go in to your property. This means that you could benefit from a better experience in the shower! When we choose the size of the combination boiler it’s very rare that we look at the heating sid. we would rather focus our attention on demand on the boiler for hot water, as most of the combination boilers are adequately equipped on the heating side regardless. For example, a 2 bedroom flat with 6 existing radiators will require about 10.5kw, whereas the smallest combination boiler is 19Kw!
It’s different story on the hot water side of things. Small combination boilers will only deliver about 9.5L/min with 30c temp. That’s not enough for an epic shower! So, in most cases we will definitely recommend getting a bigger boiler which will produce more hot water.

What to do if some of the installed or existing radiators are not getting hot enough?

There are a few trade secrets that we will share with you (Shhh, don’t tell our competitors!)
1. Increase temperature on the boiler
2. Make sure the pump its set to maximum speed (and also check if it’s not overflowing after adjustment!)
3. Balance the radiator – the most crucial thing of all. If some of the radiators get super hot in no time then turn them right down, almost to the closed position. This allows a slither of water to flow through them. You can achieve that by taking the little plastic cap off and turning the knob clockwise – that’s the opposite side of the thermostatic valve, if you got one. For the pump and boiler it’s always easier to push the water to the radiators with minimum resistance on the way, rather than pushing the water to further radiators.
Still not working? We’d be happy to assist.

Should I repair the old boiler or get a replacement?

There are three strikes if you consider repairing your old boiler. If you went through that then please consider a replacement. We know that times can be tough, but you will undoubtedly save money in the long run.  If your boiler falls under band “D” and below (SEDBUK efficiency rating you will save serious money on gas bills. You may even cancel insurance cover or British Gas boiler cover, as the chances of something going wrong would then be very low and you would be covered by the manufacture warranty.

How long will it take to replace my boiler?

If you decided to do a full conversion – gravity to combination (sealed) then it shouldn’t take us longer than 2 days. Combination boiler to combination replacement takes about 1 day on average.

Corrosion inhibitor after installation, why is it so important?

Every time the water from a central heating system has been drained down the corrosion inhibitor (such as Fernox F1 or sentinel X100) it has to be added on the next top up. Water, metal and air when combined create corrosion and that eventually ends up in the boiler heat exchanger. To prevent that’s a corrosion inhibitor has to be added. That stops the whole process in its tracks, making for a clean, safe central heating system.

Why Valiant or Worcester?

About 70% of our work is in boiler repair, along with other common heating and plumbing tasks.  That means that we know the boiler market very well and it’s easy for us to draw the line between good boilers and problematic ones. Choosing Valliant or Worcester and being their accredited installer as a company was a dream come true for us. After years of boiler installations, Valiant and Worcester appliances have never let us down. They use quality components which are user friendly, and when it comes to repair every component is easy to reach and replace (making Express Boilers staff members a very happy team!). Other brands of boilers can be a real challenge. If we have to dismantle components to get to the right valve then that means more time on the clock. These brands helps us save both time and money for you.