1 pipe radiator system & ancient radiators.

Norman_bn23

Hi all, ok been told my existing heating system is 1pipe and the servvowarm radiators need changing as they will not work with a new gas combi boiler.

Does that sound about right ?

Many thanks.

Sandtree

Which is your question, that you have a one pipe system or that such a system won't work with a combiboiler?

NSG666

Did all 4 say the same thing?

One pipe systems exist and will work.

The Servowarm boiler being replaced will be ancient and so too will the existing radiators unless they have been replaced. The recommendation to replace the radiators might be necessary if they definitely will not withstand the pressurised system of a new combi or might be precautionary given their age and that they might not withstand the pressure.

On balance, have them replaced and TRVs fitted especially as you saved money on the asbestos issue.

Jeepers_Creepers

Hi Norman.

Will they 'work'? Yes. Will they work as well as a 2-pipe system? No.

If you can bite the bullet, go for a re-piping along with new, larger, rads.

The reasons are; a one-pipe system relies on a very hot water temp in order to be able to maintain that temp throughout its length, so that the last rads on the system still receive adequately hot water. That's fine with an older, non-condensing, boiler - you just crank it up until it's kettling away, and bask in the warmth.

When you fit a condensing boiler, two things will happen - one is that you can't get such a high delivery temp in the first place (I dunno, but I'm guessing they'll struggle to go much higher than 80oC?) but the other issue is that, in order to have all your rads nicely hot, the return water temp will also have to be kept high - and for a condensing boiler, that means it won't condense very much = much higher energy bills.

So, you run the risk of (a) not having your rads as hot in the first place, and (b) not receiving the energy savings from fitting a modern condensing boiler.

Modern boilers also monitor and regulate the flow and return temps very carefully in order to have the burner running at the best, most efficient and comfortable, rate - they don't just turn their flame 'on and off' like old boilers, but instead have a full range of control over how much flame there is; they 'modulate', just like you turn a gas hob up and down in order to keep a pan simmering after it's come to the boil. With your old boiler, you can probably just crank it up to max and get on with it - the thermostat is just that, a blunt temp tool that you control, just like a gas hob burner coming on at 'max', with the only other setting being 'off'! A modern boiler, however, will take on board what you are asking of it ("Yeah, yeah - I know you've turned up the boiler temp... sheeesh...") but will then monitor the flow and return temps to try and arrive at the most efficient performance. If it sees the return temp getting close to the flow, it'll likely start to back down the flow temp, so the rads at the end of your 1-pipe chain could lose out.

That is the gist of the issue.

And I speak as someone with a 1-pipe system on a modern condensing combi, who regrets not having converted it to 2-pipe at the time (but house needing reno along with 1 year old and baby on the way made some compromises inevitable...). Does my system 'work'? Well, yes, but the rads are not as hot as they were with the old floor-mounted Mexico we found in the house (and which used to kettle away to itself all day long, and which had an enamelled flue that would strip your skin if you brushed against it), and the last rad in the system - in my son's bedroom - struggles (and fails) to heat his room properly in winter, and there's not much I can do about that (short of replacing it with a much larger rad, which I ain't going to do...).

Since the future of heating is to operate at lower water temps - and condensing boilers were the start of that, and heat pumps take it to the next level - then the sensible thing to do is to upsize your rads. They don't necessarily need to be physically larger in terms of height and width, but can be more efficient with the use of extra fins and panels. A 'larger' rad - one with a higher rated output - will give you the SAME heat output whilst running at a lower water temp.

If you can do it, I'd definitely recommend doing so. I regret my decision.

rob7475

As advised, it's better to run a two pipe system if you can do it without too much disruption. I had our boiler replaced with a combi years ago and after the change some of the radiators didn't get very hot. We found some of the radiators were on a one pipe system. After converting the sections to two pipe to match the rest of the house, they worked fine.

Jeepers_Creepers

Another issue, Norman, is that the installer may well only proceed with an agreed disclaimer - 'if your CH isn't as hot and effective as it was before, we have warned you why, and it ain't our fault.'

Another_Level

Cant see the property but re piping it to a 2 pipe system, is highly recommended.  How did the survey operative discover its a one pipe system ? 
Servo warm radiators Yes change them as well, there not so good on pressurised systems. Servo warm radiators (there quiet distinctive) its a good call from the survey man.

So your new boiler is turning into a complete new system  Its a good investment