Do I need a 'bubble tester'?

Published: Friday, 04 May 2018

AS A Gas Safe registered marine LPG installer, I frequently receive phone calls from boat owners asking me to fit a ‘bubble tester’ to their boats, writes Graham Freeman.

My initial response to such enquiries is: “Why do you think you need a ‘bubble tester’?” and (sadly) the majority reply: “My BSS Examiner tells me I need one because the rules have changed."...

bubble testerMake an informed decision

The purpose of this article is to supply some background information on ‘bubble testers’ (which are more correctly termed ‘LPG leak detectors’) and to provide boat owners thinking of fitting one with a few pros and cons to enable them to make an informed decision as to whether a leak detector can be practically implemented on their boat. All views expressed in this article are personal and not those of the Boat Safety Scheme.

Firstly, let’s debunk a myth: the rules have not changed - you donot need to have an LPG leak detector fitted to your boat to pass a BSS Examination. If you are told that you need one by a BSS Examiner, report the individual to the BSS Office (0333 202 1000). The circumstances under which LPG leak detectors may be used and by whom are explained later in this article.

What is an LPG Leak Detector and how does it work?

An LPG leak detector is a simple mechanical device which is fitted in the craft’s LPG pipework (as close as possible to the regulator). The device comprises two gas connections (in and out), a chamber containing a viscous fluid and a ‘button’ (usually red) which, when depressed, diverts the flow of LPG via the fluid chamber. If a leak is present anywhere downstream of the device (in pipework, hoses, appliances, joints etc) a bubble/bubbles will be visible in the fluid chamber.

When a leak is present, the time it takes for a bubble to form is dependent upon several variables such as diameter and length of the boat’s pipework, the length of time the button is pressed and lastly, the size (rate) of the leak. If you have a 70-footer with a forepeak gas locker and a stern galley, an LPG leak may take several minutes to form a bubble (assuming you can easily observe the fluid chamber, don’t blink, or have your finger ‘go to sleep’).


The type of LPG leak detectors currently found on boats were originally produced for the caravan and RV market where LPG pipework is small-bore, short length and feeds comparatively small cooking appliance (in kW terms). Access to the leak detector in such vehicles is easy—the owner opens the caravan or RV gas locker and presses the red button; the fluid chamber is not difficult to view, and the length/size of the pipework means that depression of the red button is limited to some 30 seconds.

By contrast, the 70ft narrowboat mentioned above may have a cratch fitted and the location of the leak detector in the pipework may involve some (uncomfortable) antics to sight the fluid chamber and press the button for up to eight minutes (yes, eight minutes!) to be confident that the boat doesn’t have an LPG leak. If, however your boat has a cruiser-stern layout with a stern gas locker and a rear galley, access to the device, the length/size of pipework, easy sight of the fluid chamber means button-pressing time can be significantly reduced.


If what you’ve read so far has made you question the utility of these devices, there’s more to consider!... Remember the comment about these devices coming from the caravan and RV world where these vehicles tend to have small (kW rated) cooking appliances (and maybe an LPG boiler feeding hot water and heating systems); then contrast this with a modern widebeam with a gas-hungry 20kW (yes, 20kW) range cooker and you’ll understand why a device that comes equipped to match up with small bore 8mm or 10mm pipework might struggle!

To ensure that the (competent) individual fitting such a device is properly aware of their operating limitations, the manufacturers' installation instructions stipulate that the device can handle a maximum (downstream) appliance load of 12kW when fitted in-line. If your boat has an LPG appliance load that exceeds 12kW, alternative arrangements must be made to ensure these devices can be safely used within their design criteria. One alternative is to fit the device in an ‘isolated branch’ which involves placing it in a pipework tangle with isolation valves which must be operated to bring the leak detector into play and then operated again to isolate it from the mainline.

You also need to bear in mind that an ‘isolated branch’ isn’t small and its configuration will, in the case of a forepeak gas locker, invariably locate the device in a position where the red button is difficult to reach and viewing of the fluid chamber will be a challenge. While stern gas lockers may not impose the same access and/or visibility constraints, such lockers are invariably too small to accommodate the cylinders in a manner that ensures that the isolated branch pipework and fittings are safe from physical damage.

RCD Criteria:

If you have a boat built to the RCD, you need to be aware that all new craft (and those under going major modification to their LPG systems) must be fitted with:

♦ A simple means to test the LPG system for leakage before use of any appliances (eg: a pressure gauge, bubble leak tester).

♦ Where a bubble leak detector is fitted in the LPG system, it shall be securely mounted in the low-pressure side of the LPG system and in the cylinder housing or cylinder locker.

(Ref: BS EN ISO 10239 clause 4.5)

The ISO also requires that information on how to use a ‘bubble leak detector/gauge is included in the craft’s ‘Owner’s Manual’ along with safety-related guidance on what to do should a leak be detected.

So, if your boat has had a leak detector fitted (in-line) from new and the boat (as supplied) had a total LPG appliance load of more than 12kW, you need to contact your builder to establish why your boat’s LPG system is ‘At Risk’. This situation does not apply to a gauge (which is fitted between the cylinder and the regulator).

BSS Criteria:

To reiterate, you do not need an LPG leak detector (or a gauge) fitted to your boat to pass a BSS Examination. However, if you don’t have a leak detector fitted to your boat and your boat is ‘in-scope of the UK gas regulations’—ie: a hire boat, commercial boat, or a live-aboard/rented boat, your BSS Examiner must be Gas Safe registered (or the Examiner must witness the test performed by a boats-qualified Gas Safe registered operative at the time of the Examination).

If your boat is ‘in‑scope’ of the UK gas regulations, please remember that LPG-related work can only be carried out by a certified and competent individual. Performing DIY gas work on an ‘in‑scope’ boat is illegal and prosecutions by the HSE in this regard are on the increase.


This article started off with the question 'Do I need a bubble tester?'. Hopefully, you are now a bit more informed on the what, why, when and how associated with the fitment, use and utility of these devices. If you have a leak detector fitted in the main LPG line in your boat and your total appliance load exceeds 12kW, your LPG systems is ‘At Risk’ and you are strongly recommended to seek the advice of a boats-qualified Gas Safe registered marine LPG operative.

Please keep your personal safety at the top of your priority list and employ a properly qualified and experienced LPG installer to perform any gas work on your boat. When you employ such an individual, check his credentials—ask to see his Gas Safe card, check that it correctly identifies the individual, is in date and, most importantly, turn his card over and check that the word ‘Boats’ appears under the LPG column and that he is qualified to work on the appliances fitted to your boat (eg: cookers, central heating boilers and water heaters).

To quote the words of the current Gas Safe campaign: