Wet radiator central heating and combi boilers
Wet radiator central heating and combi boilers
Author
Discussion

Skyedriver

Original Poster:

22,184 posts

305 months

Sunday 23rd May 2010
quotequote all
Sorry, yet another question, it might be easier if you all came round to the house project......
We have a (very old, oil fired) combi boiler that feeds a number of radiators through mainly 8mm pipework. Being a combi there is no header tank. I presume therefore that mains pressure keeps it working, does that mean that if I turn off the mains at the stop cock, I can remove the odd valve or cut and re-route the pipework better. Its been "surface" mounted in any place with no thought for appearance.
Thanks everyone.

daveparry

988 posts

223 months

Sunday 23rd May 2010
quotequote all
a combi has an expansion tank and is usually pressurised to 1.5 bar, turning off the mains stopcock will have no effect on this but it will have an effect on your hot water, you won't get any!

If you want to make changes to your system (radiators) you will need to drain down and make sure to repressurize afterwards not forgetting to bleed rads.

Ferg

15,242 posts

280 months

Monday 24th May 2010
quotequote all
Bear in mind that with a pressurised system once you drop the pressure to zero you can often work on it without draining as the vacuum holds the water in. Obviously soldering is out, but you could cap it while you get the rad repositioned and the pipework done then finish with a couple of compression couplings.

Skyedriver

Original Poster:

22,184 posts

305 months

Tuesday 25th May 2010
quotequote all
Hmmm, thanks guys. Was intending to cut and re route a few pipes and also fit thermostatic valves. How will the system re pressurise itself/how do I do that more likely. Will obviously bleed the system fully once all re connected.
Thanks
Tony H

Ferg

15,242 posts

280 months

Tuesday 25th May 2010
quotequote all
It's repressurised with a filling loop which is a removeable section of pipe joining the mains cold water to the heating system. Normally stainless braided rubber hose, it's sometimes built into the boiler.

Skyedriver

Original Poster:

22,184 posts

305 months

Tuesday 25th May 2010
quotequote all
Thanks Ferg
Presumably as long as I dont lose too much water it'll refill and maintain pressure? It's a very old oil boiler and due for replacement but financed are currently being directed to a full property refurb and as the boiler still works......it'll have to survive a little longer. Guess if it doesn't work afterwards I can get a boiler man to come and service it one last time.
ps Getting told that 8mm systems and fittings etc are being discontinued because they block up with silt etc but everyone who i speak to that has 8mm has never had any trouble with them....
pps How easy is it to straighten and rebend old 8mm pipe. Will it just crack?
ppps Do the 90 degree compression bends cause too much restriction to the flow rather than a gently bent pipe? Looking to tidy up messy pipework and pull it in towards the wall it was originally "thrown" against.

Ferg

15,242 posts

280 months

Wednesday 26th May 2010
quotequote all
You can re-bend microbore, it's Table W copper which is quite soft. You can kink it of you get the bends too tight though, so do it all carefully.
Microbore systems have never been a good idea. Aside from the sludge issue they are difficult to add to and of course they are difficult to make look any good.
Elbows are never a great idea on microbore, but it depends on the system and how good the flow is at that point.

As far as the boiler is concerned, I think you're stressing over nothing. I'd drain the whole system if it's microbore and give it a good flush out by filling and draining once or twice. Filling pressurised systems is easy. Open the filling loop tap and watch the gauge..
Yes, there is a possibility the boiler might fail, but no real reason why it should.

Skyedriver

Original Poster:

22,184 posts

305 months

Wednesday 26th May 2010
quotequote all
Thanks agan Ferg.
Yes there are a couple of slight kinks in the pipes that I want to take out when I re route.
Haven't taken any covers off the old boiler as yet, it just sits there like a rusty old lump in the corner of the currently semi derelict kitchen. Spoke to the guy who used to service it every year and he told me that whilst it worked it had a number of faults and ommisions and that others have been called out between his services. Access isn't its best feature either. Plan is to keep it working during the summe months (oil tank nearing empty too but needs moving) and get it sorted after the rewire, new windows, extension, kitchen, bathroom, fire place,multi fuel stove, redecoration, and before winter returns!! No pressure then.
Cheers
Should I just go all electric??????