Combi replacing old open vent system - should existing CH pipework be replaced?

[rbel]

About to have 30 years old open vent system replaced with Vaillant combi. One of the heating company bods providing quotes has indicated that the existing CH pipework (half buried in floor slab, other half in void beneath timber floors) should be replaced as the increase in pressure could result in leaks. Is this a valid point or a tactic to make the job a bit bigger than it needs to be?

My initial thoughts are to install the new boiler and see what happens when the system is commissioned.

Grateful for any comments based on experience.

-- rbel

[Chris Bartram]

My Mom had this done about 5 years ago, and the pipework and rads dated from about 20 years before that: no problems. Conversely, mine has always been pressurised since installation about 18 years ago, and failed in the concrete floor a couple of years ago.

Personally, I'd give it a go....

[gremlin_95]

If it's correctly sized, I wouldn't worry too much. We have old pipework that is over 25 years old and it is completely leak free even though it has been a pressurised system for nearly 4 years now.

[Dave Liquorice]

Well the pipe work in the ground floor is going to be at not far short of 1 bar in an open vented system in a two storey house and header tank in the loft...

I was a bit concerned about the DHW side here when the thermal store went in and thus the DHW went from open vented to mains pressure (around 4.5 bar) but I haven't found any leaks. Taps that require more force than I like to stop dripping yes but no leaky pipework and the standard of work is not the highest. We are talking about pipework done around 30 years ago...

[John Rumm]

The most likely failure points would be the old lockshield valves and the rads themselves rather than the pipework. If the pipework buried in the slab was not adequately protected from the cement in the slab, then there would be some merit in replacing those sections.

(this is assuming that the layout is in other respects acceptable).

Either way it will need thorough flushing and cleaning before the new boiler is commissioned.

Probably what I would do also. In fact you would be able to test the pipework before the new boiler goes in.

[Lobster]

Which is what happened to me - over a couple of weeks after the installation two old radiators developed rust pinhole leaks in the middle of what were apparently intact panels. Everything else was fine (this was ~10 years ago)

David

[David WE Roberts]

I'm contemplating much the same thing. I have (tentatively) decided to replace everything.

People have said that their systems are still good after 20+ years which is fair comment. On our system, the radiators are of different vintages, as are the thermostatic valves. The thermostatic valves are showing the most wear and tear.

However this is a major refurbishment, and the question for us is "Will the system still be as good in another 20 years?" because we don't want to be replacing stuff 10+ years down the line unless we have to.

I suspect some central heating systems may date at least partly back to the

1970s and must have a finite life.

Oh, and replacing the bodys for the thermostatic valves is an interesting challenge. As far as I can see you have to chop back the existing copper and fit in a new short piece of pipe unless you are 100% certain that the old nut and olive are good for another 20 years.

Cheers

Dave R

[rbel]

Many thanks for all your thoughts. To respond to some of them - the property is a bungalow so the current head is around 2.5 metres.

There has not been any sign of leaks or weeping from valve glands but I cannot vouch for the state of the copper in the concrete slab other than again there is no apparent sign of leakage.

Power flushing is included in my spec for the job.

I decided on a combi because I want the space currently used by a large DHW cylinder for a decent size walk in shower. We are lucky to have very soft water - straight off Dartmoor.

While the lockshield valves are all originals I installed Drayton thermostatic valves about 12 years ago so with a bit of luck these will still be OK.

Hopefully all will cope with the increased pressure but if not I have a back up plan to run new pipework down through built in cupboards etc and move a couple of the radiators and there should still be sufficient time to implement this before the colder weather returns, if it becomes essential.

-- rbel