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NB, Pressure Vessel = Expansion Vessel.

Turn the boiler off at the mains.

Find the PV valve, which looks like a car tyre valve with just a threaded part sticking out. The PV is often red. They can usually be accessed from the top of the boiler or behind the front drop-panel. Some boilers such as Ravenheat can be impossible to access!

If water comes out when you press the central pin, you need a new PV :cry:

Find a drain cock on the pipes somewhere, or on the boiler. DO NOT use the pressure relief valve, or it WILL leak afterwards. If you can't find one you can use a radiator bleed point, but that's in a pinch, because you'll be letting several litres of water out.
Drain enough water from the system to drop the water pressure as read on the boiler gauge, to Zero. Close the drain cock.

Use any (eg car or bike) air pump to pump up the PV to eg 10 psi (0.7 bar).
Some boiler instructions or those with knowledge about the individual system might give different figures. It isn't critical but don't go above 1 bar 15psi.

Remove and refit your pump to see how much the pressure drops when you remove it and inevitably lose some air.
If the pump doesn't have a built in gauge, pump it up a bit high, then keep taking readings with a push-on gauge. Every time you do, the pressure will drop a bit.

It's important that you don't rely on the reading that you get as you pump into a "closed" system - as the wet side starts to pressurise it'll give you a meaningless reading on the dry side you're pumping into.

When you get to 10psi, undo your drain cock again. If there was still water in the PV, your air pressure will force it out. If that happens, recheck the pressure and pump more, and repeat until undoing the drain cock doesn't give you a spurt of water. You can now rely on your air pressure reading.

The PV may be say 10 litres. If it was full of water you have to displace all of that water from the system side, by your pumping up the air in the vessel. That's a whole bucket of water!

Fill the boiler water back up to 1 bar pressure, slowly, and switch the boiler back on.

The air shouldn't be able to get into the radiator system because of the rubber diaphragm in the PV.
If you bleed your radiators, you will have to top up the water in the boiler via the filling loop, but not the air in the PV.

DO NOT let water into a hot boiler. Let it cool first.

DO NOT let water in too quickly. 20 seconds for 0.5 to 1 bar should be OK.

DO NOT take the water pressure above 1.5 bar- even if the system is warm. If it doesn't cure your "Low Pressure" indication, the switch may have stuck. Leave it an hour or two - water may force its way through dirt to get to the switch and turn it on.

DO NOT allow the water pressure to go too high when refilling Turn it off early to see if the gauge keeps rising a bit.

NEVER use the Pressure Relief Valve to let water out of a system – it will leak afterwards!

If the pressure relief valve was leaking before you repressurised the PV, it will probably continue to do so and need replacing.


If by that you mean can he sign everything as though he'd installed it: No, it would be illegal, because he didn't.

If you HAVE the situation of a boiler you need to be made "legitimate" then a GSR engineer technically would have to remove and reinstall it, and flush clean and refill the system with inhibitor. Then he could say he'd installed it, notify it to GSR and Building Control, and fill out the Guarantee forms.
GSR have now issued Technical Bulletin covering what has to be done if a RGI finds this situation. Many RGI's wouldn't touch it.

Also be aware that if you don't have all the paperwork in place, you can expect to find that manufacturers' warranties, and service contracts such as British Gas 3 Star, are void.

The Gas Safe Register has now replaced Corgi, but the rules are the same.
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Because it CAN!

The design of most current fittings isn't very good. Basin wastes come with nothing to stop water running down the grooves of the threaded part.

The two commonest solutions are to use sanitary silicone between the thread and the ceramic of the basin, or to use a Basin Mate.


This replaces the rubber washer which goes against the bottom surface of the basin.
They cost a couple of pounds and are available at many plumbers' merchants.
They squash down to about 12mm thick.

Links are dead - requires updating.
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IN the news - again.
If the thermostat in a hot water cylinder fails, the cistern (tank) in the loft can soften and dump 250kg of near boiling water through the ceiling. This has caused death several times in the last few years.
This is how it happens:

New design thermostats were introduced in 2004. If you haven't changed the immersion heater or its thermostat since then, you will have the old type. When those fail, they fail "on" which means there's nothing to stop the water boiling.
The post 2004 thermostats have an extra safety thermostat built-in, which switches off if the temperature of the water gets above the normal range. It does NOT reset itself when the water cools.
They can be easily fitted by someone competent to do basic electrical connecting, and only cost a few pounds. It's a totally "dry" procedure!
Once the wires are removed from the terminals, the thermostat simply slides out. The replacement should be the same length as the one which comes out The're shorter than you might think, eg an 18 inch thermostat goes in a 27 inch immersion heater, which you'd find in the top of a 36 inch high cylinder.
The new 'stat will have the same two terminals, no extra ones.

Dead links removed
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5 ) Combis - Combination Boilers - Do I want one?

Combination boilers provide heat for CH, for up to about a 6 bedroomed house, and hot tap water on demand.
They range from about 23 to 42 kW, and are usually chosen according to the hot water requirement. More kW = more or hotter hot water.

Unlimited hot water, though the CH stops while the tap is on.
Save space - no need for any storage tanks
Cheap to install, though a conversion from a traditional system will usually cost more than a conventional boiler-only replacement.
No pumps are needed for mains pressure hot water

If they go wrong, you have no backup such as immersion heater for hot water.
You do need a good mains supply.

If you want to benefit fully from a higher output combi, you need an unusually good mains supply!

Even then the taps lower in the house will be favoured if two are on together, so you might go short in the shower upstairs.
A thermostatic shower valve should stop you freezing, but the flow may go right down.

Even in the best situations a combi will only supply about two taps at once, with careful plumbing, and devices such as flow restrictors. Most plumbers won't know much about these.
If you want extra high pressure or flow of hot water, you would probably be better off using a tank of stored water, and either relying on mains pressure, or pumping it.
6 ) How much gas am I using?

You can measure this at the meter.
There are two main types of meter in use:

1) Imperial meters, where there's a dial with a needle going round marked 1 cu ft

Measure the time it takes to do one full revolution, in seconds, call that "T". Remember that 1 minute 20 is 80 seconds, not 120 seconds - an easy mistake to make.
Work out the calculation :
1092 divided by "T".
That's the rate you're using gas at, in kW.
So if it takes 40 seconds, you're burning at a RATE OF 27.3 kW.

If it burns at that rate for two hours, that's 54.6kW hours

2) Metric meters. These have numeric displays, measuring in cubic metres.

One cubic metre would read
(0's then) 1.000 on the display, the decimal point is always 3 digits from the right.
Measure the usage in 2 minutes, using the rightmost 3 digits. Remember it might go past zero. You'll have an answer like
0.XYZ cubic metres.
Multiply that figure by 321
That's how much you're using, in kW.
So if you've used
0.085 cubic metres in 2 minutes, that's 27.3 kW.
Again that's the RATE of gas usage.
If it burns at that rate for two hours, that's 54.6kW hours

Appliances use more gas than they produce energy, because they aren't 100% efficient, so the figures above might be for a "24kW" boiler.

Be aware that if the boiler can't get rid of its heat fast enough, it might well "modulate" which means turn itself down. (This could eg be due to restricted tap water flow through a combi.)

Pro's will argue about the precise figures, because they do depend on the "calorific value" of the gas, which varies. It'll be stated on your gas bill, in MJ/m³.

YOUR gas meter might not look quite like either of these. The important thing is to notice whether it's Imperial (cubic feet) or Metric, (cubic meters).

This is a list of particularly dangerous boilers.

Some boilers on this list have let poisonous carbon monoxide into the room, killing the occupants.
This is not an exhaustive list.

Knowledge and special equipment is required to test them, and anyone without it is strongly advised not to do anything which disturbs the boiler case. Call a GSR Registered Installer.


Even with a boiler not on this list, breaking a case seal means you have to test it afterwards. If you aren't technically speaking "Competent", or don't have the equipment to do it, then you're breaking the law.

Link dead. If in doubt ask your installer. This particularly applies to old Netaheat, and old Thorn boilers, and a few others.
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8 ) Pumping Over

This is the term used when water comes out of the Vent Pipe into the Feed and Expansion Cistern. The water then goes down the Feed Pipe and round the system.

It's a very BAD THING, because it oxygenates the water which causes rapid corrosion in the system.
It can be caused by poor pipe layout. The normal flow of water causes the pressure in the circuit where the Vent Pipe joins, to be slightly higher than that where the Feed Pipe joins. The water levels start equal, so it takes very little resistance in the circuit to make the water come out of the Vent Pipe.

It can be alleviated by increasing the height of the inverted "U" of the vent pipe, though if the Vent and Feed pipes join within about 150mm of each other this should not be necessary.
In a typical flat with a concrete ceiling, there often isn't much room for the vent pipe. The level of the water in the f&e tank should only be about 100mm - at about the level of Freddie fish's mouth. So the top of the curve of the vent pipe can be at least 250mm, say, above the resting water level. That should be anough.

Another very common cause for Pumping Over, in older systems, is a build-up of a hard scale, made of iron, calcium and other extracts from the system water. This causes a hard blockage of the pipe, nearly always at the point where the Feed Pipe joins the system. Often this can only be cleared by cutting out and replacing the pipe.
Powerflushing may well not be enough.

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9) Gas Safe Register

From April 1st 2009 CORGI will no longer hold the register for qualified gas installers.
The new body is called the "Gas Safe Register" http://www.gassaferegister.co.uk/

Other than the change of name, particularly from the consumer point of view, the role is the same as Corgi's.

The Corgi name, unfortunately, doesn't belong to the government so a company called Corgi will continue to exist. That may, or may not, be of use to gas installers but will be of no particular relevance to consumers.

For the time being, the same requirements will exist for people wishing to become Gas Installers. It will continue to be through the ACS system.
The current scheme is outlined below:

Gas Services Installation and Maintenance ACS aligned N/SVQ

This method of certification is awarded by City and Guilds and has a scheme number of 6012; this is currently the only N/SVQ that has been aligned to the ACS scheme and is accepted by both GSR and the Health and Safety Executive (HSE).

This scheme is for the installation and maintenance of natural gas appliances & equipment and Emergency Service Operations.

The N/SVQ certification is valid for GSR Registration purposes for a period of five years from the date the certificate is issued and allows the operative to access and take the required ACS re-assessment due at that time.

Entry Routes for Operatives seeking ACS Certification
Prior to assessment every certification body has to ensure that each candidate provides accurate information relating to any gas industry experience and/or qualifications held.

During the processing period each candidate, depending upon their experience/qualification(s) held is allocated into one of three categories, these are -

Category One

Experienced gas-fitting operatives from within or outside of the United Kingdom who are:
seeking to renew expired or expiring certificates of gas safety competence i.e. HSC, ACoP, ACS or Gas Services N/SVQ's
seeking assessment and certification to extend their range of gas work;
foreign nationals seeking to obtain certificates of gas safety competence that will allow them to meet United Kingdom gas work requirements. Operatives in this category need to provide evidence of their gas fitting qualifications and experience and all information needs to be translated into English, where appropriate.

Category Two

Candidates have to provide evidence that qualifications are held which are relevant to the area(s) of gas work where they are seeking to acquire certification. These qualifications must show that competence has been achieved in the generic work activities associated with fossil fuelled appliances/equipment and/or pipe work installation, including any of the following work activities, flueing or ventilation or the installation, maintenance or commissioning of such appliances.
Examples of appropriate qualifications include:
  • Plumbing craft qualification or N/SVQ (oil and/or solid fuel options) - suitable initially for domestic or commercial central, water heating or pipe work installation.
    Pipe Fitter/Welder craft qualification or N/SVQ - suitable initially for commercial pipe work, pipe work commissioning and meter installation.
    Heating and Ventilation craft qualification or N/SVQ - suitable initially for commercial pipe work and appliance installation.
    Refrigeration Engineer/Fitter craft qualification or N/SVQ - suitable initially for commercial appliance and pipe work installation.
In addition to appropriate qualifications candidates need to provide written evidence confirming that "on the job" gas installation and/or maintenance training has been undertaken and that any experience of gas work gained has been carried out under the direct supervision of a competent operative, employed by a GSR registered company. Such written evidence will need to be provided from the employer and detail precisely the areas of gas work undertaken.

Category Three

These candidates are new entrants into the gas industry and are unable to provide details of relevant qualifications and/or experience. These will be individuals who are classed as entering the industry for the first time, or changing career direction.

Candidates in this category should be advised to seek training and experience that will result in the attainment of a National/Scottish Vocational Qualification (N/SVQ) in Gas Services, Installation and Maintenance at Level 2 or 3, or obtain employment with a GSR registered business who is willing to provide an auditable extended period of company "in house" gas training programme together with the necessary organisational support prior to undertaking ACS assessment.

The duration and content of the training programme will be determined by the scope of gas work being undertaken. Evidence in the form of a portfolio following completion of such training must be presented to the assessment centre before a candidate can undertake assessments.

Alternatively an N/SVQ within the Mechanical Engineering Sector with related on the job gas training and experience in the intended areas of gas work to be carried out will also support a future application.
Application for GSR Registration

It is important to note that prior to applying for GSR registration, you or your gas operative must be in possession of valid certificate(s) of gas safety competence for the categories of gas work in which you will be working.

If certificates of competence are not in place GSR will be unable to process the application. Once you have passed your assessments, you can apply for an application pack from GSR. After applying for registration, providing you meet the necessary requirements, a GSR Inspector will carry out a Pre-registration assessment visit. On completion of the pre-registration process, GSR decides whether your application will be accepted or not.

GSR registration is valid for a year from April through to March. All registered installers necessarily renew their registration in March. GSR sends out notification.

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