Has anyone had a combi conversion with microbore?

kittennose

Vortigern said:

kittennose said:

Looking at converting our system to a combi, but stressed about costly leaks given our pipework is 8mm microbore and 30+ years old.

Has anyone had this done successfully?

Yes, original 1988 system changed from open vent cylinder with feed & expansion, to combi.  No issues with leakage.

How much of your pipework is microbore? Mine was 22mm flow & return from boiler to cylinder, then 15mm distribution and finally a short length of coiled 8mm to each radiators. You don't see the 15mm pipe until you take some floorboards up.

Not sure, ours goes into the actual walls

kittennose

Maybe I should take some floorboards up - our 8mm pipes all go into the walls though, not the floor. That's why leaks stress me out.

ThisIsWeird

What will lifting floorboards achieve? Unless you leave them up for a few weeks after the conversion.
If you are really concerned, to the point of you not being able to relax after the work, then insist on a pressure test as FreeBear suggested. Your new system should not get above 3bar at any time, even during faults - the boiler will have a safety release valve set at that -  so a, say, 5 bar test should give you complete peace of mind. 

FreeBear

ThisIsWeird said: If you are really concerned, to the point of you not being able to relax after the work, then insist on a pressure test as FreeBear suggested. Your new system should not get above 3bar at any time, even during faults - the boiler will have a safety release valve set at that -  so a, say, 5 bar test should give you complete peace of mind. 

BS EN 14276 is (I believe) the standard that covers plumbing & heating systems - One normally conducts a pressure test at between 1.5 & 2 times the maximum working pressure of the system. So if the boiler safety valve lifts at 3 bar, the test on the rest of the system should be at 4.5-6 bar.

Radiators, pipes, and fittings are generally certified for a maximum of 10 bar, so a 5 bar test pressure is generally accepted as reasonable. Any plumber familiar with installing underfloor heating should be equipped to do pressure tests on a heating.