Knowledge Centre

Boiler pressure low

Boiler pressure dropping! What are the causes of losing boiler pressure ?

Boiler pressure low

Boiler pressure safety switch Vaillant Eco-tec.

A guide to why your system pressure  is dropping? Do not ignore this!

Boiler pressure dropping is something we encounter very frequently, especially during the heating season.

Central heating system which incorporate a pressure gauge and a filling loop are called sealed systems and should not lose pressure consistently.

Sealed system means exactly that!

Once all the air is bleed out of the heating system the pressure in the system should stay stable because the water has no where to go.

The central heating water circulates around the radiators and boiler every time you turn it on and unless you bleed a radiator or you have a leak the water has no way of escaping.

Boiler pressure dropping, what are the causes of system pressure lose?

The following steps will guide you through some basic steps to understand what is causing this drop.

If you cannot resolve this yourself using our guide below we are on hand to step in should you require some professional intervention.

1-You have a leak on your heating system!

You have a leak somewhere on the central heating circuit! This includes radiators, radiators valves and all connecting pipework.

Unfortunately this does sometimes mean pipework which is not visible, either underneath timber floors or screed.

Customer action! -Check all visible joints including radiator valves and connections for obvious signs of leaks. If you feel confident in doing so turn off the isolation valves for the heating circuit underneath the boiler as shown below. This will temporarily leave you without heating however this will prove whether your leak is on the heating circuit or boiler. If the pressure stays stable after shutting off the valves and you cannot find any obvious leaks then your leak is in the floor somewhere and you may require our assistance.


2-You have a faulty pressure relief valve!

You have a faulty pressure relief valve either inside the boiler or on an external pressure relief valve. Pressure relief valves are designed to let out excess pressure in the event of over pressure usually when the boiler exceeds 3 bar. When they fail they will leak water from the central heating system at a much lower pressure to a copper pipe terminated outside of the property.

Customer action!- Look externally for a small copper pipe exiting your property usually close to the boiler or cylinder location. This is the pressure relief pipe exiting to atmosphere.

You are looking to see if this is dripping while you have pressure in the system. If it is call us, this is not a DIY job.

3-You have a faulty expansion vessel

You have a faulty expansion vessel- This means your boiler pressure will exceed 3 bar during the heating up process.

This is because the expansion of water in the system has nowhere to go due to the expansion vessel failure. Pressure  increases exponentially with temperature so once  the pressure reaches 3 bar the pressure relief valve will expel the excess pressure from the system until it reaches a safe point. When the system cools down you will find the water lost will now show on the pressure gauge as a significant drop. Very similar to the above scenarios, as if the system has a leak and will also cause the boiler to lock out and break down once cooled.

Customer action!-Run the central heating system up to full temperature and check to see if the pressure gauge rises. If it does shut the boiler off immediately and contact us. Replacing an expansion vessel is not a DIY job either. It is also good practice to replace the pressure relief valve at the same time.

This is due to the wear and tear caused from the valve opening and shutting and may not reset once its been activated too many times.

4-The leak is inside the boiler!

The leak is inside the boiler! Weak points on boilers are as follows: Automatic air vents,  O rings joints, washers, divertor valves and heat exchnagers.

In most cases the boiler leak will eventually drip out of the bottom and be quite obvious but in not in all cases. Small Internal leaks do not always leak

out of the boiler because the drip may be dripping onto another surface which is catching the leak.

The leak can also be disguised by running down a pipe which may not be obvious or the leak can  evaporate while the boiler is hot.

Customer action!- If you see a leak coming from the bottom of the boiler turn the electrical supply off to the boiler immediately as the leak can very easy leak into the electrical control box of the boiler and inflict expensive damage. If you have followed all the other steps and by a process of elimination come to the conclusion that the leak is inside the boiler, call us.  We will service the boiler and provide a quote to repair the leak.

Do not take the case off of the boiler yourself in any circumstances as this may contravene Gas safety regulations.

5-You have bled the air out of your radiators!

You have bled your radiator system to remove air from the the top of a radiator. In turn this drops the system pressure and must be replaced by introducing fresh water into the system via the filling loop.

Customer Action!- If you have never done this before there are many You tube video tutorials.

Here is one for an Vaillant Eco-tec plus boiler which has an internal filling loop.

There are many to choose from including the tutorials from on our own You Tube channel.  Remember when re-pressurising a system after bleeding radiators, take care to not over presssurise the system.  To be on the safe side, stick to 1 bar of pressure and then monitor for two weeks to ensure you do not have any leaks on the system which may have lead to the air to build up in the tops of the radiators in the first place.

I hope this guide has been helpful.

If you do have further questions or would like a site visit please contact us. We are more than happy to provide advice over the phone which costs nothing.

Written by Dean Dawe MD

Combi Boilers

Combi Boilers – What are the pros and cons?

Combi Boilers, the pros and cons… this is a question I get asked a lot when helping customers choose the right boiler for their property.
Hopefully this article will help to make the facts a bit clearer so you can understand the pros and cons of a combi boiler installation before making a decision.
Many people I go and see will say to me right from the off ‘I would like a combi boiler please’ without really understanding the negative aspects of a combi verses other choices that may be available.

Combi Boilers

Combi Boilers – The Pros ✔

☻      A Combi boiler in most cases removes the requirement for a cold water storage tank in the loft. This is because the previously stored cold water services from the tank are converted onto the mains supply dramatically increasing the pressure to taps and showers in the house.

☻      Removing the water tank also frees up space in the loft for storage or a conversion leaving you with whats called a dry loft. No water services in the loft reduces the risk of water tanks or pipework leaking through the ceiling in future so provides peace of mind!

☻  As part of a combi boiler conversion the hot water cylinder is also usually removed, freeing up a handy storage space.

☻ A combi boiler provides hot water on demand, in other words when the hot tap is turned on the boiler will fire and send hot water to the tap. In theory you should only be paying for the hot water you use and need. With a traditional hot water system the boiler heats the cylinder and the stored water sits there until it is drawn off, so there is always the risk of water being heated unnecessarily, if not exhausted before it cools down.

☻ A combi boiler also increases the hot water pressure to all taps and showers, which once combined with the increased cold water pressure is a big perk of removing your tank fed system. Showers will automatically become power showers, compared to a standard non pumped traditional system and taps miraculously come to life!

☻ Due to the cold water main now being the primary source to all taps, you can now drink it! Very handy in the night should you wish to grab a drink of water and your bathroom is closer to your bedroom than the kitchen.


Combi Boilers – The Cons ✘

☹   Combi Boilers can only provide a limited volume of hot water to taps and showers, therefore unsuitable for properties with more than two bathrooms. If a combi boiler for instance, can deliver 18 litres per minute, which is about the maximum performance achievable right now, the 18 litres per minute has to be shared between what ever is being drawn off it. For example, with this boiler you could run two showers, each one achieving 9 litres per minute flow rate. If you were for instance running a bath, all of the performance (18 litres per minute) would be required to run that bath in a sensible amount of time. 

☹ Combi boilers and mains water systems in general are totally reliant on the pressure and flow rate to the house. It needs to be adequate enough to cope with all the cold water and hot water running from the same supply. The classic mistake we see, many plumbers do not check this first and install combination boilers in houses which should never have had the cold water storage tank removed in the first place due to low mains water flow rate. So, if you have 12 litres per minute coming into your property and your combi boiler is sized to heat 12 litres per minute, as soon as someone else turns on another tap in the house or a washing machine, it will starve the combi boiler of water. If this happens and you are in the shower, it will just trickle out for a while or stop completely until full pressure is restored to the shower. 

Here is the simple test we do on a site survey to check you have adequate flow rate to your house. 

☹ Combi boilers do not have a back up, so in the event that the boiler breaks, in most cases you will lose both heating and hot water until the boiler is repaired.

Bringing your hot water and heating into one nice neat box does have its downsides. Some clients negate this by also Installing an electric shower which does not need the boiler to provide hot water and will work independently. 

☹ Hot water will take a long time to reach taps or showers when hot water draw offs are a considerable distance away from the combi boiler.

This can be  frustrating and wastes water on a grand scale! TIP-Look at the proposed location for the combi boiler and then the furthest tap away from the boiler location. If for example you are thinking of Installing combi boiler on on the ground floor of a town house and there is  a bathroom on the 2nd floor you will experience this problem and worth avoiding . This is the reason why hot water cylinders are usually sited in the central of  property to distribute hot water quickly to the taps.

☹ Combi boilers are much more prone to scaling up as the plate heat exchanger fitted to this type of boiler have very narrow water ways. This can be addressed by fitting  water softeners and magnetic system filters on the heating side. A clean combi boiler is a happy boiler!

☹ Modern combi boilers do not have as long a life span as a traditional system and they can become inefficient to repair near the end of their life. The best advice is to get the longest manufacturers warranty you can at the outset and keep the boiler regularly maintained with an annual boiler service. A good quality combination boiler depending on the amount of use should last 10 to 12 years.

I hope this article has been informative and although this post was not meant as an advert we would of course welcome anybody who is thinking of upgrading their boiler to contact us via the contact page or give us a call on 0800 2851920.

The purpose of this article is to educate and provide honest advice based on the facts and 25 years in the business. If you feel it has done that please LIKE AND SHARE the article from our Facebook page.

Thank you, Dean