GAS – the inside info… v5

This page provides some inside information that I hope will help you understand key issues of your heating system and therefore make informed choices when considering a new boiler.


You should not do work on anything for which you are not qualified. Always get expert advice from qualified trade’s people. Acquire Home Services (Stephen Ford) accepts no liability for your actions as result of reading these pages.


The details I present here are the sort of things that gas operatives wish the public knew because it would make the gas operative’s life easier! The information is such that when I tell my customers, they say “I wish I’d known that before. Why didn’t the other gas operative ever mention that?” I hope it will make your life safer and easier.


I have written these notes based on my experiences during typical day-to-day work.


Inside information tends to be such that you would never guess in a million years because… well, because if you are not in the trade you wouldn’t know. And let’s face it most people want to get on with life, their hobbies, holidays and so on. Who wants to search the web about plumbing and heating? It’s up to the gas operative to inform you… to put it in front of you, because unless we do, you will be completely unaware. Yes?


For example -:


 If you would like me to write about a heating, plumbing or electrical issue not covered here please feel free to contact me.


My aims for writing these notes include -:



You can search this text using crtl + F. Some hyperlinks have been provided here -:




Central heating





What is a service? What is a repair?


A service is checking and adjusting an appliance that is otherwise running safely and as designed. The aim is to find any faults, adjust settings as needed, check that ventilation is correct, check that there are no gas leaks, and check that the installation is as per the manufacturer’s instructions.


A repair is the correction of faults with the appliance and / or installation. The cost of a repair will depend on the price of parts and the gas operative’s fees.


Sometimes a customer will book a service and when the gas operative arrives he finds the boiler is broken. The customer mistakenly expects the faults to be repaired during the service and for the same cost as the service.


What should happen in a Service?

Sometimes I will be getting on with a service, checking for gas leaks and doing all the jobs I know should be done and the customer will say something like -:


“Why are you looking at the gas meter? The other gas operative didn’t do that”, or


“Why is it taking so long? The other gas operative only took ten minutes.”


A service includes checking many things and it takes time. I have seen lots of instances when services have clearly not been done comprehensively or correctly. Customers rightly want an explanation why previous gas operatives have not done everything they should have and of course I have to say that I can’t account for their practices.


During a gas appliance service the gas operative should do at least the following -:


1              Ask about all the gas appliances and take a quick look at them all to ensure there is nothing overtly wrong even with the ones he is not servicing.

2              Check the gas meter for correct installation; that it’s secure, and the Emergency Control Valve (ECV) is accessible and labelled properly.

3              Make sure there are no leaks in the pipework and that the gas pressure is correct when the gas appliance(s) is operating.

4              Refer to the manufacturer’s instructions to establish the gas pressures and gas usage figures for the appliance.

5              Check the ventilation. Without the correct ventilation, the appliance may produce Carbon Monoxide (CO).

6              Check that the flue and terminal can be inspected throughout its entire length.

7              Service the appliance.

8              Check there is the correct amount of gas being used by the appliance and adjust as necessary.


If this takes less than an hour, I personally would question whether the appliance has been serviced correctly.


Manufacturer’s Instructions

The manufacturer’s instructions are very important. They are useful for the customer and the gas operative. By getting hold of a copy and making them available to your gas operative, you help him do his job well. They are there to be read – read them and find out what the correct service process is. If you don’t understand any of its contents then, ask your gas operative to explain. Please remember that he has the next job to go to…


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I have presented a range of information below about boiler installation issues and the way they work…


Condensing boilers & Radiators

A condensing boiler will only condense properly if the radiators and bypass valve are set up properly.

The radiators need the lock-shield valve turning down so that the water leaving it is at around 55°C. This means that the water returning to the boiler will be roughly 55°C and it should condense really effectively.


Which Boiler type?

“You need a combi luv…” Have you ever been sold a boiler without being asked how your heating and hot water fits into your life? Have you had a combination boiler (a combi) fitted because the installer said it was a good idea? How do you know which boiler is good for you? The following table provides a few answers and issues for consideration.


Here are some definitions for the combi and heat-only boiler.


COMBI – this boiler type is a “combination” of an instantaneous hot water heater (turn on the hot tap and the boiler lights and gives you hot water) and a central heating boiler. It is only of any great use when you don’t have room for hot water storage OR when the cost of the waste heat from hot water storage is significant. There is no other good reason to fit a combination boiler.


HEAT-ONLY – this is the type of boiler that heats water in your radiators and in the water storage unit (eg a hot water cylinder).


The following table really refers to the overall heating system but that is specific to the boiler type so maybe it’s a moot point whether the pros and cons are for the boiler only or the boiler and heating system.





Cost to install


If an old heat-only system is removed then this is an additional cost.


Cost to run



Cost to maintain

Same as heat-only

Same as combi

Cost to repair

Same as heat-only if an Intergas.

High if an ED type  (See water section below)

Same as an Intergas combi.

Much cheaper than an ED type combi.


Keeps the heating system very simple. Less to go wrong.

Far more complex. Has valves and controls and a hot water cylinder for providing hot water. May need lots of cold water storage if high flow rates are required ie three or more bathrooms. Pumps may be needed.


Has a limit to the amount of hot water. A 40kW boiler is required for two 10 litres per minute outlets.

Very effective but relatively costly to install, run and maintain.

Waste energy (heat)

Minimises the loss of heat from the hot water because it heats it as needed.

Heat continuously lost from the water storage unit.

Water section

This provides hot water in some combi designs. See the discussion below


On break down

No hot water or heating

Hot water if immersion heater fitted and working…!

Gas supply

Needs a large gas pipe. It will probably need a new one because they were installed under-size in times gone by.

May not need a new gas pipe if replaced with a smaller condensing boiler. In this case you may get away with the old pipe even if it was under-sized with the old boiler.



The water section

As of 2015 when I discovered the Intergas range of boilers, I have changed my opinion about the wisdom of installing a combi based on its reliability compared to a heat-only boiler.


All other combis manufactured in the UK have a water section which provides the hot water. It comprises many components and is therefore less reliable than a boiler without those fittings. I call this the English Design (ED) combi. The Intergas uses the primary heat exchanger to heat both the central heating and the hot water and therefore does not need the ED water section. It therefore has to be more reliable. And there are other features about its design which improves its survivability when it’s not looked after but I haven’t discussed those issues here.


 It’s still true that if it breaks down you have nothing… no heating and no hot water. However if a combi is reliable (Eg the Intergas range) then you should have little to be concerned about. It would be wise to have spare electric heaters just in case but that could be seen as applicable to all boiler types. I have a leaflet about the Intergas combi which I will send on request.


Continuing about the typical issues with a combi installation – If you change to a combi you will probably need a new, bigger gas pipe installing. If the old boiler is a combi, then the chances are the gas pipe will be too small. I suggest you have it checked.



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Central heating

Bypass valve

The bypass valve allows water to circulate around the boiler and some of the adjacent pipework even when the controls are satisfied and are no heat is required. In this event there can still be excess heat in the boiler which has to be dissipated, and to achieve this the boiler may keep the pump running after a heating cycle.


If the pump is inside the boiler, the boiler may have a built-in bypass. It’s as well to have this checked. Providing the bypass is adjusted properly, this type of arrangement tends to look after itself.


If the pump is external to the boiler then you will need to establish whether you have a fixed bypass, an automatic or none. To do this, trace the pipe from the boiler to the pump. Then beyond the pump in the direction of flow, you are looking for a pipe, possibly with a hand-wheel before any other valves which allows water to go back to the boiler without passing through the heating system.


If there is a valve and it has a hand-wheel, then it needs replacing. If the valve has a dial-type knob on it, then it could be automatic (that is spring loaded, which is best).


If it’s a fixed valve it is very inefficient. The bypass needs to be fully open when it is required to do its job and allow hot water to flow straight back to the boiler. However, when heating is required it needs to be fully closed to make all the water go from the boiler to the heating system. If it’s fixed, it can’t be fully open and fully closed simultaneously. If it’s automatic it opens and closes when necessary.


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Filling loops

A filling loop is used on a pressurised central heating system. It transfers  your fresh drinking water into the heating system. For this to happen, the drinking water supply has to be connected temporarily to the heating system.


Please bear in mind that your drinking water is also your neighbour’s drinking water too. And theirs is yours… When connected to the heating system it’s connected to a source of poisonous water which may contain rust, sealing compounds and corrosion inhibitors. So disconnection should be done as soon as the heating system has been filled. It’s not unusual to see the temporary hose left connected.


How do you know if your system is pressurised? The boiler will probably have a pressure gauge, or show a pressure in a digital display. There will not be a small tank in the loft or anywhere else (although there could be a large cold water tank).


The filling loop can be a tap on fixed copper pipework (where you “top up the water”); it could be a shiny flexible steel-braided hose with a valve at either end; it could be a key that you fit into the bottom of the boiler and turn to let water in; or some other connecting device.


The point is that on one side of the filling loop is your fresh drinking water and on the other are you central heating pipes possibly full of poisonous corrosion inhibitors. And if the hose, key or other connector is in place and / or connected, then you have got your fresh drinking water connected to pipes with poison in them. In this condition you are hoping the valves don’t leak… !!



·         Always disconnect the hose, key or other connector after filling / pressurising your system.

·         BUT… check that the filling loop is installed properly because if not and you disconnect you could cause a lot of water damage. In this case get an gas operative in to fix it before disconnecting.

·         If the disconnected filling loop drips, then get it fixed. A leak is the very reason you don’t want the loop connected.


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Probably the most significant risk with electrics is FIRE.


A domestic electrical system should be checked every ten years.


Your Electrical Earth

It could be you haven’t a clue what the earth cable is. You may never have looked inside a three-pin plug; you may never have realised that the earthing arrangements in your house are there to save your life, and protect your property…


The earthing system in the house must be connected to the supply to the house for an earthing arrangement to work.


If a live cable breaks off inside an appliance with a metal case and the cable touches the case and there is no earthing system, the metal case will become electrically live. If you touch the case when it is live it is the same as touching a bare, live electrical cable. The chances are you will receive a shock… with possible fatal results…


If the earthing system is in good condition, and the above short circuit occurs, a current flows through the earth wire under what is called ‘short circuit’ conditions. The current is instantaneously so high that it should cause the circuit fuse to blow, or the miniature circuit breaker to ‘trip’. This stops the appliance from being electrically live and removes the risk of an electrical shock.


For this to work, the electrical earthing system must be designed and installed properly.


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