Worcester Gas Safe Installer

Combi Boiler Constantly Loosing Water Pressure?


One of the most common faults we come across as gas engineers in regards to combi boilers is low pressure. Now as a home own it can get very frustrating when you find you are having to constantly top up your boiler’s pressure.

Normally on a sealed system you should only have to add pressure after you have bled radiators or maybe once a year or so. If you find it is becoming a regular occurrence then you have a problem.

There are a few reasons why your system can be losing pressure however it all comes down to the same issue- you have a leak!

Now this isn’t necessarily something to worry about. A very small leak can cause pressure to drop from 2 to 0 in a couple of weeks the best thing to do is start looking around for any signs of escape.


PRV Discharge Pipe

When it comes to a system that is ways loosing water pressure the first place as gasmen we check is the PRV Discharge Pipe. It will be a small pipe coming out of your wall and should be turned back to the wall as seen across:

Look for signs that the pipe is, or has been leaking. This can sometimes be as small as a little drip however this will cause your system to loose pressure over time.

If it is leaking you will require a replacement pressure relief valve and possibly some attention on your expansion vessel. Give us a call on (01782) 811102 and we can give you a quote to repair/ replace it. We will need your boiler make/model and either the serial number or GC number to get the correct part.

Under no circumstances should you try to block the pipe, this is a safety valve for the boiler and doing so could be extremely dangerous!

Leaks From Radiators or Valves

The next thing I would recommend to check is whether any of your radiators or radiator valves are leaking/ corroded. This can sometimes be more obvious than you would think due to lime scale build ups. If something has been leaking for a while scale can build up forming a green/brown ‘fluffy’ build up.

If you have any signs of this the most cost effective solution is a replacement valve.

It is a good idea to check all of your valves as you can sometimes have several leaks, it is also cheaper to change a few valves at once; saving you money on time and labor.

Next look at your radiators and check for similar signs but from bleed nipples, edges or sometimes the bottom where sludge has corroded through.

Look for signs of rust.

This can sometimes be a simple repair, just replacing the bleed nipple. Sometimes however it could require you to have a radiator replacement. Holdcroft Heating can give fantastic quotes for radiator replacements using the leading brands such as Stelrad and Myson, each offering a 10 year warranty respectively.

Concealed Leaks

These are the most tricky and expensive to find. If you have checked your radiators and discharge pipes and everything seems fine, you now have the possibility that your leak is either in the boiler itself or under your floors.

Both of which will require you to have an engineer out to try and find it. This could be as simple as checking in the boiler or as intrusive as lifting carpets and floorboards to try and find the leak. Even then- if you have concrete floors with buried pipes it could be impossible to find the leak.

There are products on the market designed to seal small leaks in systems however they are not a guaranteed fix, however if you have tried everything and are at the end of your tether they would be well worth a go.

I would recommend something like Fernox F4.


Hopefully this helps you to do some basic checks to help narrow down where you are l osing your pressure. If all else fails you can always get an engineer to call and check for you however you can save money by running through some of the checks above yourself so we can find and fix your problem quickly.

If you are still having problems and would like someone to call and look at the system for you please contact us to book an appointment. Holdcroft Heating are a family run business based in Burslem Stoke-on-Trent. We pride ourselves on going the extra mile for our customers and aim to give the best possible service for an affordable and fair price.

Contact us on: 01782 811102

Or request an appointment at: sales@holdcroftheating.com

Affordable Luxury for the UK's most reliable boilers.