Boiler replacement, need to replace all pipework?


Postby u2fan » Tue Mar 16, 2010 12:44 pm

We have gas central heating and gravity fed hot water run by an old back boiler in the fireplace that needs replacing. We understand that condensing boilers are no longer made to fit behind fireplaces so we have no option but to re-position the new one on an outside wall (in the same room).
All existing copper pipework was installed approx 1977. New pipework will of course be needed from the gas meter to the new boiler etc. We've been informed that it will be necessary to replace all the pipework from the boiler to the airing cupboard upstairs, rather than just join on to the existing, as apparently the old pipework would not be up to standard. Is this correct? If so, there would be a huge amount of disruption due to fitted shelves, heavy furniture etc. What is the difference between old and new copper piping?
Any advice would be much appreciated.
PS Any recommendations for the most reliable make of boiler?
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Postby htg engineer » Wed Mar 24, 2010 10:49 am

You can get condensing back boilers that have a fire-front.

It is best to replace the pipework, why are you changing the boiler ? you have to bear in mind that the pipework will be the same age - possibly older, so any crap in the boiler will also be in the pipework. The waterways on modern boilers are alot smaller for efficiency, so will become blocked quicker.

Even with new pipework it is essential to flush the system and add inhibitors. Also your old system is probably not pressurised, will the pipework hold out at 3 bar on a pressurised system ? if not it could cause major water damage to your property

It is your decision though, if you want a new boiler connected to old pipework, as long as the flow and return are 22mm, and the gas pipework is adequate (minimum 22mm pipe). Ask around you'll find someone to do it - but they can't guarantee old pipework.


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Postby u2fan » Mon Mar 29, 2010 7:54 am

Thank you for the advice - very helpful and you've explained it well.
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Postby Perry525 » Fri Apr 02, 2010 2:59 pm

When you say you have an old back boiler that needs replacing, have you considered how much a new one will cost? Is it not better to wait until it fails before spending a lot of money?
Have you checked on the net for spares?
The chances are that your pipework is perfectly OK.
Changing from a gravity system to a pumped system, the addition of a pump/circulator for a few pounds will probably solve your problem?
Where I live for example, the water is clean, it is soft and there are never any calcium deposits on any of our taps, washing machine or dishwasher.
Before you dump your existing set up do look at it carefully.
Copper pipe does not wear out, joints made correctly will last for ever.
If you cannot do the work yourself, do get a detailed specification from whoever you chose for the job. As mentioned elsewhere the correct sized pipes make a very large difference.
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Postby u2fan » Sun Apr 04, 2010 11:16 am

Thanks for the advice.
The system is working at present but the boiler is extremely noisy and is nowhere near as efficient as modern boilers.

Recently the pilot went out and would not stay alight. New thermocouple needed though only replaced about 3 years ago. Engineer advised boiler needs replacing and is not even worth servicing. He said the reason thermocouple wears out is due to crap in the system. Other engineers have previously serviced boiler regularly, every 2 years normally.

Pipework was installed by previous owner who was a competent gas engineer so I know done to a good standard. Have not yet checked the diameter of the pipes but am aware must be 22mm. We do have a central heating pump.

We think that it might be time to bite the bullet and get the boiler replaced rather than wait until it conks out when we really need it. Also, better to do it before we have done even more decorating and varnishing of floorboards in other rooms etc. We have not seen new condensing boilers that fit behind a fireplace so would be interested to hear about any. We do not use the gas fire at the front as the room is always warm.

The real dilemna is whether or not to change the pipework as advised. Assuming the pipe diameter is satisfacory, will the good quality joins withstand the pressure of a modern system? Can a pressure test be done? Only thing is how would we know if there is a small leak without all the pipes exposed?

Any advice would be much appreciated.
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Postby Perry525 » Mon Apr 05, 2010 2:01 pm

When your boiler was made, it was probably sold as 80% efficient, a modern boiler will be sold as about 90 to 95%. The problem here is that none of these boilers is checked by any one, they are merely self certified by the manufacturer. The so called improvements, are basically that some of the heat that would otherwise be lost, is captured and recycled.....but, this only happens during start up and the benefit disappears once the system is up to running temperature.

Thermocouples are made of copper, they are subject to a lot of heat (being in the flames) and the copper does evaporate. What he says is rubbish.

Some boilers, fitted with cast iron heat exchangers go on for over thirty years and as long as spares are available I advise people to keep them, as they are better made than today's.

The servicing of a boiler is like anything else, it depends on how well it was made and how hard and how long it works each year.

The pipe to and from the hot water tank on a gravity feed system should be at least 28mm.
How well it will work depends on how many bends and what temperature, how well insulated, the internal friction being the main consideration.

Gravity systems are old technology, they were OK 50-70 years ago when people had more time, today a pumped system produces hot water so much quicker. Switching the pipe work so that the hot tank is part of the central heating system will resolve this for you at little to no cost.

It is true that whenever a boiler gives up, its a disaster, but modern systems, usually fail on their exhaust/heat exchanger fan, or computer control system. Older ones are so much simpler.

If you merely T off the existing central heating with a 22mm pipe and a tank thermostat, for a few pounds you will immediately see and feel the difference. If later you decide to change the boiler, then the existing system will work.

Your existing boiler is a floor level on the ground floor? The cold water expansion tank is in the loft, the difference in feet between the bottom of the boiler and the surface of the water in the expansion tank is about 18 to 20 feet?

Most modern pressurized boilers are expected to run at one bar or thereabouts, this equals a column of water 30 feet high, they do run at half a bar = 15 feet. From this you can see that there is very little difference between what you have and a new boiler. By all means measure the height of the water in your system and compare it with the boiler of your choice.
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Postby u2fan » Tue Apr 06, 2010 12:18 pm

Thanks again for the advice.

I may not have been too precise on the details of our current system so here's some more info.

It is a Potterton Fireside 51 back boiler positioned on the ground floor behind the gas fire in the fireplace. We do have a hot water cylinder (with it's own thermostat strapped to it I think) in the airing cupboard upstairs. I believe that it is part of the central heating system but do not know enough to say for sure. There is a time control switch that allows us to have only the hot water on, or water and heating, but cannot have just heating without hot water.

The reason I said it is a gravity system is because the cold water expansion tank is in the loft but I could be wrong. (Distance is probably about 18 - 20 feet as you say). I don't think there is a pump that works with the hot water system, but there is a central heating pump positioned near the boiler.

We are quite happy with the heating we have and the water temperature and pressure is fine. The boiler makes very loud banging noises but we are used to it. I know that generally older equipment can be better than new but obviously was taking the advice of the heating engineer. The boiler has lasted so far for 33 years with only a few thermocouples replaced and a new ignition switch so it must be good.

In view of the above, is your advice as to T off and tank thermo still relevant?

Thanks again as you have certainly re-assured us.
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Postby ktitley » Mon Apr 12, 2010 7:33 pm

yes you can get condensing back boilers but a wallmounted one would be cheaper
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