It is frustrating and disturbing when your boiler goes out of pressure. That could be when you are experiencing cold radiators, the pressure gauge is indicating low or that you are no longer getting your heating. This guide gives reasons why this occurs, the most frequent reasons, easy tests that you can carry out, and when you need to seek the assistance of a professional.
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What Does it Mean by Boiler Pressure and what should be the Optimal Level?
Ideal Boiler Pressure in the UK
Most boilers work best between 1.0 and 1.5 bar when cold and around 1.5 bar when hot. All boilers have their manuals, which tell you the exact figure.
The Importance of Pressure
Pressure would assist in pushing hot water through your heats. Too low it will not circulate and too high might lead to leaks or trips.
Symptoms of Low Pressure in Decaying Power Boilers
- Boiler pressure keeps dropping on the gauge.
- There is some heating and then cold radiators are seen.
- Boiler presents a code of error or closes down.
- Night pressure or post heating.
Important: In case you notice the above listed signs, continue reading to get probable causes or you can also read our detailed guide: Learn how to fix pressure in the UK.
Common Causes of Low Boiler Pressure
These are the most common causes of a boiler to lose its pressure:
- Small Leaks in the System
Slowly depleting pressure will be a leak in any part of the heating system (pipes, radiators, valves). Even a small leak under any radiator may lead to the problems in several weeks.
- Radiator Bleeding
Radiators with the help of bleeding release trapped air. Pressure may fall off, in case you have bled a lot of radiators and you have not repressurised.
- Broken Pressure Relief Valve (PRV)
The PRV is opened when the pressure becomes too high. In case it is clogged or broken, it can cause water to flow out and lose pressure.
- Expansion Vessel Problems
When the water is heated, the expansion vessel absorbs varying pressure. Loss of air charge in it or diaphragm failure can result in a drop in pressure.
- Filling Loop Issues
Unless the filling loop (the tap that adds water) is not worn or switched off, then your boiler cannot fill up the system.
- Internal Boiler Leak
Internal components of the boiler can leak like heat exchangers. Without an engineer these are more difficult to notice.
- Combi Boiler Specifics
Combi boilers are also more sensitive to pressure loss. If you have a combi boiler losing pressure, it could be the internal components, the hot water plate heat exchanger, or a leak in the system.
- Overnight Pressure Drops
A small boiler leakage or a defective seal, which only leaks when the system pressure goes down may be the cause of your boiler pressure reducing overnight.
Checks You can do Now (Step-By-Step)
hese are simple checks that one can safely attempt prior to panicking;
1. Look For Visible Leaks
Scan radiators, pipes which can be seen and below the boiler wet patches. Even small drips matter. In case of a leakage, note down the position and take photographs.
2. Check the Pressure Gauge
Read the boiler gauge at a temperature of zero.
Is it below 1.0 bar? If yes, it needs topping up.
3. Have You Bled Radiators Recently?
Pressure tends to go down, when you simply bleed the radiators. You will have to repressurise the system.
4. Check the Overflow Pipe
Locate the small plastic pipe at the boiler where the outflow of water is drained through the PRV. When it is wet or dripping, the PRV can fail.
5. The Pressure Overnight
Record the pressure both in the evening and in the morning. When it drops only at night then it will indicate a tiny slow leak.
6. How to Repressurise a Boiler (Basic Guide)
You know that you can repressurise a boiler yourself. If unsure, call an engineer.
7. Location of Filling Loop
This tends to be a silver flexible hose under the boiler and has a valve at each end.
8. Activate the Filling Valve
Turn the valve until the pressure gauge is increased to approximately 1.2 – 1.5 bar. Close both valves tightly.
9. Check Leaks
After repressurising, observe the gauge and take a few hours. In case of a second drop in pressure, then you have a chronic problem.
Pro Tip: If you are not sure, then get a qualified Gas Safe engineer. For example, in the case of electric boilers, an approved heating engineer or electrician should be used .
When there is no Visible Leak, what could it be?
Sometimes the boiler might be losing pressure. The no leak scenario is confusing. Here are the likely causes;
- Internal Boiler Leak
Water may also leak into the boiler housing and evaporate, so you are not able to see it.
- Malfunctioning Expansion Vessel
This may cause pressure to be dropped without any outward symptoms.
- Defective PRV
In the situation where PRV releases water gradually, the overflow may drain away without notice.
- Corroded Radiator Valves
They have the tendency of slowly leaking at valve stems.
Combi Boiler Losing Pressure
The combi boilers are prevalent in homes in the UK, though they have certain weak areas:
- Plate Heat Exchanger Leaks
In case of this failure the pressure reduces and you may have lost hot water within no time.
- Diverter Valve Issues
This may lead to pressure and hot water errors.
- More Sensitive Systems
Combi systems consist of small sealed circuits that are more responsive to leakages.
Note: Most of the same causes are applicable to a Worcester boiler that is losing pressure or any other brand.
How to Fix if the Boiler is Losing Pressure
The following are the simplest ways to make technical fixes;
- Repressurise the System (DIY)
See steps mentioned above.
- Tighten Visible Leaks
Tighten small joint nuts with PTFE tape or confidently tighten. For major leaks, call a pro.
- Install New Valves
Faulty Radiator valves or filling loops can be replaced.
- Install PRV or Expansion Vessel
These components normally require a certified engineer.
- Repair Internal Boiler Leaks
It usually involves replacement of parts or in old boilers replacing the boiler.
At What Point to Think about Replacement of the Boiler
In case the cost of repair is high or the boiler is more than 10-15 years old, then replacement can prove to be a more economical option in the long term. New boilers are more efficient and cheaper to heat. You can refer to the following;
Grants and Assistance
In case a replacement is the appropriate solution, grants and schemes may be beneficial. Home Energy Guide is specialised in government grants, like ECO4 and BUS. For Scotland homeowners, boiler grants are also available.
When to Shut the Boiler and Call an Engineer
- Severe leakages, vapour or flooding – Switch it off promptly and contact an expert.
- Loss of pressure that persists following repressurising – Call a Gas Safe engineer.
- Sweet odours, sounding bangs or the visible destruction – Suspend the use of the boiler and request assistance.
The Role Home Energy Guide can Play
Home Energy Guide is an initiative aimed at assisting the UK homeowners and tenants in comprehending the help offered by grants in terms of upgrading and replacing the boiler. In case of expensive repairs or when your boiler keeps losing the pressure you could be eligible to get a grant to replace an old or an inefficient boiler. Check your eligibility now!
Contact Home Energy Guide to check eligibility status, obtain a free quote now on any possible upgrades that may be free or reduced cost and also aid with the application process.
When DIY vs To Call an Engineer
DIY No problem
Repressurising, solving visible leaks, and bleeding radiators.
Call an Engineer if
You detect a new drop in pressure following having replenished the pressure, anesthetic concealed leak, PRV failure or expansion vessel failure, or dreary finds. In case of gas boilers, always use a Gas Safe engineer.
Worcester Boiler Losing Pressure
Boilers in the UK homes are of Worcester. The reasons and corrections are identical: test the filling loop, PRV, expansion vessel and potential undercover leakages.
Quick Troubleshooting Pre-flight Inspection Checklist (Summary)
- Test the mock: less than 1.0 bar?
- Check at the radiators, pipes and beneath the boiler to see whether there are any visible leaks.
- Have you had any recent hemorrhage of radiators? Top up pressure if so.
- Repressurise through the filling loop to approximately 1.2 – 1.5 bar.
- Monitors pressure overnight to identify exceptional slow leaks.
Note: In case it continues to go down, then seek the services of a qualified engineer.
Frequently Asked Questions (FAQs)
Overnight pressure usually indicates a minor leak or an issue is exhibited upon cooling of the system. Look to see whether it has drip drops and watch the run-off. In case you are unable to locate a leak, have an engineer examine the PRV and expansion vessel.
In case you can safely repressurise the drop being small, then short-term use is normally fine. Yet frequent falls indicate some hidden defect. Make sure to seek professional diagnosis by way of safety and efficiency.
Symptoms such as a sudden increase or decrease in pressure, pressure decreasing as the system cools or the boiler losing pressure without noticeable leaks are the signs. An engineer is able to check the air charge of the vessel as well, then replace it when necessary.
It may be unseen through internal leaks or broken parts such as heat exchanger or PRV. To determine internal faults in the boiler, a Gas Safe or a qualified heating engineer will be required to inspect the boiler.
Simple repairs such as repressurising or changing minor components will be cheap. Significant repairs or replacement boilers are more expensive. In case of replacement, ensure options of checking grants using Home Energy Guide to minimise expenses.
Check the boiler pressure after every one month and bleeding radiators. Also check where a plumbing job has been done or where there is a strange behaviour of the heating system. Regular checks help spot issues early.
