Replacing a Traditional Floor Standing Boiler with a Wall Mounted System Boiler


Postby Lima7 » Wed Nov 26, 2014 9:55 pm

Hi,

I want to replace a traditional floor-standing gas boiler (pumped radiators and gravity fed hot water system) with a new wall mounted system boiler.

I’ve checked the plumbing behind the boiler and am reasonably confident that that I’ve identified the various pipes. There’s an out and return pair that I believe go up to the upstairs radiators, and there’s 2nd pair that go under the floor to the downstairs radiators. There’s also a pair of very large pipes one of which goes up into the ceiling, I believe this is the gravity feed to the hot water tank, I think this goes into the ceiling, under the upstairs floor, across to the airing cupboard down through the boiler, and then back across the scullery floor to the boiler.

I’ve had an engineer out to quote for a new boiler, what I don’t understand is he’s quite insistent that the old gravity pipes to/from the hot water tank will need to be replaced, but to be honest I just don’t understand why. I understand that the new system will have to all pumped, I understand that a valve will need to be installed to control the flow of water between radiator circuits and the hot water tank, but I just don’t understand why the water can’t be pumped through the old gravity pipes? The engineer was talking about ripping up the floor and ceiling for new pipes, all of which costs time and money (and mess). The engineer seemed quite genuine, but without a full understanding of the issues I was a little suspicious I was being fed a line, the best answers I could get out of him was that the ‘design isn’t up to modern standards’ and ‘the pipes need to be upgraded’ but without any explanation that I could understand.

A second question is am I better off with a System boiler, or a traditional ‘standard’ boiler? The house and radiators probably date from the 70’s or 80’s I understand that system boilers operate at higher pressure than standard boilers, and I’ve read that there’s a danger of the increased pressure causing leaks in an old system. Do system boilers really offer any advantages over standard boilers, other than dispensing with the tank in the attic? Would I be best to just replace with another ‘standard’ boiler, rather than risking the extra pressure?

Thanks
Lima7
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Postby proptech » Thu Nov 27, 2014 6:42 pm

Hi Lima7

A system boiler contains all the working components. What you describe as a 'standard' boiler is known as a 'heat only' boiler despite it also supplying hot water.
Either way there's going to be a degree of system redesign. With a heat only, the pump and control valve/s are external to the boiler, often sited in the airing cupboard. The system could be open vented as you have now, or sealed in the same way as a system boiler
Without actually seeing your installation, it's not easy to advise on the best way forward, or on what your engineer is suggesting, I suspect he may be correct.

My personal choice would be for a heat only boiler, providing there is space available. That way I have a choice of the components, and any breakdowns may not have to involve the boiler.

At the end of the day, you really have to discuss the alternatives with your installer, and trust his judgement.
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Postby Lima7 » Fri Nov 28, 2014 9:22 am

Thanks for your input proptech,

As an engineer myself, I always find it hard it to accept the "just trust me" answer, I much prefer to have an understanding of the reasons for a given solution.

I guess the problem is that I know the design requires a pipe from the boiler to the hot water tank, and a second return pipe back from the tank to the boiler. I also know I already have these two pipes, what I don't understand is why the existing pipes aren't good enough and my floors and ceiling need ripping up!

I understand the need for new pipes and valves at the ends i.e. the boiler end and the hot-water tank end, I don't get the need for new pipes between the two.

The ultimate problem is that I have a very nice oak floor that I'm extremely reluctant to rip up!

Kind Regards
Lima7
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Postby proptech » Fri Nov 28, 2014 7:15 pm

OK I see your point, and yes, pipes are pipes. Obviously there is some system redesign to be done no mater what type of boiler you go for. From my point of view, I'm not there to investigate the possibilities myself, and see the site conditions.
Perhaps another installer's opinion would be an idea.

Just another suggestion - could the oak floor be skillfully lifted, rather than "ripped up"
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Postby Lima7 » Sat Nov 29, 2014 11:41 am

Thanks proptech,

I've just had two more quotes, both from engineers who seem to belong to the 'pipes is pipes' school of plumbing. Neither have suggested replacing the pipes to/from the H/W tank!

I guess either the first guy knows something the other two didn't, OR he was feeding me a line.

Thanks for your help.

Cheers
Lima7
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