Reuse open vented central heating pipes for closed pressurised

Discussion in 'Plumbers' Talk' started by fire, Mar 14, 2016.

  1. fire

    fire Well-Known Member

    Hi all

    I have a question that has been playing on my mind for ages.

    I am updating my central heating, i currently have a faulty boiler installation which is a compact open vented central heating system where the hot water tank and central heating open vented system is all combined into one complex tank.

    I am changing this system to a Combi boiler which uses a pressurised closed loop system, i am changing all the radiators but as for the old piping to the old radiators which is in good condition my question is can i re-use them.

    The current method of this piping has a single type drain off valve located in the electric cupboard in the hallway which loops round and goes into a concrete floor hence the reason why i am thinking of re-using it like this, save time and effort and money. The piping has lots of odd bends and sizes as it goes from 22mm to 15mm then back to 22mm and so on.

    Is this just an elaborated way of making a standard radiator circuit or is there some hidden science involved in the piping that would make the piping unsuitable for a closed pressurised central heating system?

    The current system has no control valves for the radiators, they are all lock-shield type of valves on both sides of each radiator with fixed non adjustable plastic caps on them. Only 6 radiators in total and all on the same floor, it is a flat.

    So all the radiators will be new, it is just the network of pipes i want to re-use, is this possible?
     
  2. Ryluer

    Ryluer Well-Known Member

    YOu can change it over to sealed but the extra pressure might find leaks in an old system. Like under the floor.
    Plenty of plumbers get caught out this way. With the customer saying "it didn't leak before you touched it".
     
  3. Can you re-use the existing pipework? Yes.

    Might it leak due to the increased pressure? Yes. It might. But no reason to believe it will.

    Usually it's the rads themselves that leak due to internal corrosion - the increased pressure finally 'pops' them! Or any compression fittings, and most of these are the actual rad valves - so if these are being replaced, you should be ok.

    Something of more concern, I'd suggest, is the presence of sludge in an old vented system. Your new boiler will not want any of that malarkey going in to it.

    When you remove a rad, see if nasty black water comes out of it when it's tipped empty.

    Also be sure that your current system is a 2-pipe type and not one-pipe (when you look under the radiators, does a pipe run between the two valves, connecting them?)
     
  4. fire

    fire Well-Known Member

    Interesting you say that.

    I drained the entire system today and removed the multi purpose tank. Wow what a construction of copper plate and tubes this tank is, rather masterful tbh.

    When i removed the tank black sludge, rust and gunk it was smelly too. It was strange as it took me some time to work it out but the two drain valves in the hallway cupboard would not drain unless the tube attached to them was acting as a syphon, as in bellow the level of the pipes. I had to run them out down the stairs and remove one of the bleed screws on the radiators. This caused the water too shoot out, the system had a strange fallen over U shaped 22mm tubing just before the second drain valve.

    There are two pipes a feed and return, i pulled the pump off which i believe was the return as it entered the boiler lower down while the other left boiler above it.
    This boiler is solid cast iron, it is heavy even for 2 people. I plan on pushing all remaining sludge out by attaching a non return valve to the flow pipe and a hose pipe to the return and out to a drain. let it run for a few minutes and drain it out again.

    I was also planning on using a sentinel 800 cleanser flush after i modify the piping to the new radiators as the new rads stand off the wall a bit more as well as the TRV valve are somewhat proud of the old locations.

    What is baffling me is this U shaped piping curling round the wall between the two and only drain valves.

    So to answer your question there does look like two tubes but they head off all over the place in that the bedroom has a send and return pipe, the diner is connected to the send buy going through the wall to this 22mm pipe in the bedroom but the send of the radiator does not go through the wall connecting to the return pipe but back down into the concrete floor.

    When you say a pipe running between them to connect them, do you mean a single pipe, the same pipe connected to both in and out of the radiator?

    The first radiator in the kitchen has two 15mm pipes going into two 22mm pipes which from what i can see are the flow and return as one pipe wired into the motor and the second 22 connected to the other side of the radiator was into the top part of the cast iron boiler.
    These 22mm pipes seemed to go directly through this cast iron boiler body and up to this tank above it which had a heat exchanging coil within it. then a sort of top chamber with another U shaped pipe and a cone shaped copper top hat, this was surrounded by water supplied from another mini tank which had a ball valve in it. All contained in one tank, really is a wonderfull thing to see, i'll take pictures tomorrow.

    The hot water was supplied from this and has no hot water cylinder, it is all inside this open topped tank.

    This U shaped piping curled around the wall looks or should i say behaves like a drainage water accelerator kind of thing to build momentum for the water to drain. I never seen anything like it before.
    The drain valves are totally worn out so they need replacing for sure.

    I really not sure about this piping, its overcomplicated to say the least but i am sure super simple for the experienced plumber.
     
  5. "When you say a pipe running between them to connect them, do you mean a single pipe, the same pipe connected to both in and out of the radiator?"

    Yes. That's the simplest way to identify a one-pipe system - which you clearly don't have. Phew.

    A photo of that weird pipe U-bend would help - I haven't a clue what it's like :)

    It's your call on whether - or how much - of this pipework you retain. In theory it all can (obviously except for the bits you won't need, like the vent and feed pipes going up to the tanks in t'loft.)

    Actually, what would probably be a useful things here is to keep a foot or so of this vent pipe in place, and remove the rest above it. Then top that pipe with an auto air vent. That should catch any trapped air that gets through the boiler that the boiler itself doesn't remove. Not essential - but a thought.

    Removing sludge is unfortunately rarely as simply as passing a hose through it - a lot will be stuck to the pipe sides so will only shift properly with chemicals and hot water.

    Mind you, most of the old sludge will be in the rads, which you are removing.

    Who's fitting the boiler anyhoo? In theory that GasSafe will want to flush your system anyway, and fit a filter (almost certainly the boiler manufacturer's requirement for warranty).
     
  6. Ryluer

    Ryluer Well-Known Member

    Sounds like something from the Victorian era. Probably needs ripping out.
     
    fire likes this.
  7. fire

    fire Well-Known Member

    As promised some pictures of this system.

    To note the tank is not in the loft, it was in the kitchen just above the boiler itself.
     

    Attached Files:

  8. If you are fitting a brand new boiler and brand new rads, then I reckon Wry is right - go for a completely new system.

    Pipes are the cheapest part of your system, so it's basically a 'labour' cost, and hopefully you can do most of this yourself.

    Use plastic pipe if it's easier (it usually is) and lag any that's under the floorboards. Bring the 'legs' up to the rads in copper - looks sooo much better (use push-fit elbows but make sure the copper is fully de-burred).

    (A wee tip - fit the last plastic pipe around a foot away from this elbow where the copper comes up through the floor. You'll then find that you have a nice amount of 'play' in your copper legs - it'll be pushable upski and downski as well as rotatable, so fitting the rad valves will be a lot easier. Obviously try and finish with the copper legs at the correct lengths so's the plastic pipe is sitting straight, but if you ever come to removing a rad (eg for decorating) having this 'play' is a great boon.)
     
    fire likes this.
  9. Is that pipe 'loop' in a small room or cupboard? It looks like a contrived 'radiator' to me (our airing cupboard has a zig-zagging pipe going up one side just for this purpose.)
     
    fire likes this.
  10. fire

    fire Well-Known Member

    Yes it turned out to be a make shift radiator...

    I have scrapped 99% of all piping, the stuff in these pipes is like soot you find in a chimney it is just wrong. I using a combination of copper and pex piping as the reason for this mess was not being able to route copper tubing around the layout of the place. PEX makes that possible as it can flow around easy, i decided to use 22mm pex pipe with 15mm copper pipe in the rooms with the pex in the loft.

    Moral of this story, do not even consider using part of an old system when installing a new one, you will just waste your time money and effort. It's all part of a experience learning curve.
     
  11. KIAB

    KIAB Super Member

    Rip it all out & start from scratch, you'll know everything is done correctly & will not leak.:rolleyes::)

    Been there,done it & been caught out.

    Best way to use 22mm as much as you can, & drops in 15mm, if I every redo the heating, I will have seperate zones for upstairs & downstairs.
     
    fire likes this.
  12. fire

    fire Well-Known Member

    Completely now agree.
    It is amazing how much battering a central heating system gets over the years, how much radiators rust from the inside out and how much sludge they develop.

    As you say, it really is not worth rescuing much, maybe a small bit of copper tube but in reality even that is pretty slim.

    That is exactly what i doing using as much 22mm in the loop with only the drops in 15mm copper, i had enough of messing around trying to rescue parts of the old heating system, I am scrapping the lot all be it maybe 1% which are the mounting holes for the radiator brackets and holes already drilled for pipe clips. No point re-drilling these holes as they are in the right place so i just removing the old plastic pipe clips and putting new ones on with new screws into the existing holes and plugs where possible.

    Neighbours already complained about noise, say it sounds like a building site every day. Well i guess it is a bit :D
     

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