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Refilling a sealed central heating system

Discussion in 'Plumbing and Central Heating' started by Whitling2k, 20 Feb 2014.

  1. Whitling2k

    Whitling2k

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    Hi,

    I am planning on draining and refilling my sealed CH system at the weekend to reconfigure some pipes and rads, and add a drain cock. It’s a large system with 20 rads!

    I have isolating valves (that do work) between my ground and first floor (where the boiler is).

    First question – should I isolate the lower half of the system and just drain that? Should I top up with inhibitor? Does it matter what make/type is already in there? Or should I drain the entire system?

    Second question – when refilling – all the advice I have read say to close all bleed valves then connect/open the filling loop – then bleed the rads once mostly full. Should I actually leave the highest radiators bleed valve open with an assistant watching for water? Otherwise – the air will just become more and more compressed and I’ll be working against it? It seems the volume of air in the radiator/system is way above the capacity of the boilers expansion vessel.

    Cheers – look forwards to hearing what your views are.
     
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  3. Whitespirit66

    Whitespirit66

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    There must be air vents on system, or it would never fill. Presuming all the work is downstairs - isolate upstairs from downstairs system - drain downstairs, opening bleed valves on d'stairs rads to assist.

    After work completed - close bleed vents, open d'stairs/upstairs isolators - fill system, bleed rads - lowest first (topping system pressure up as you go). Run system then test for leaks.

    Then drain some water from a rad and add inhibitor to it.
     
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  4. Whitling2k

    Whitling2k

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    Thanks whitespirit.

    So it doesnt matter what inhibitor may be already in there? Their websites suggest not mixing; sentinels website for example says words to the effect of only top up with fernox after a partial draindown if your system already contains fernox and not another brand of inhibitor.

    I would have thoght it's all similar stuff so can't be that much of a problem?

    And also when actually filling the system - do I leave one bleed valve open? Or should my system already have air vents? I'm confused on this point - i thought a sealed system wouldn't have any vents - hence closing all bleed valves will prevent water entering?

    Ta,

    Whitling2k
     
  5. Whitespirit66

    Whitespirit66

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    I wouldn't get too worked up over mixing inhibitors. No doubt Fernox don't want you to use other manufacturer's products in. If concerned, drain whole system, but you will be making work for yourself.

    There should be air vents on your system, either in boiler or on the high point(s) of the system's pipework.

    AUTO

    http://www.wickes.co.uk/content/ebiz/wickes/invt/221364/22mm-Auto-Air-Vent-Bottle-Trap_large.jpg

    MAN.

    http://www.toolstation.com/shop/Hea...r+Vent+Caps+Capillary+15mm/d230/sd2708/p45763
     
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  7. JBPHS

    JBPHS

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    When system is drained shortly before refilling, close both valves on a radiator ideally a towel rail. Add inhibitor to that rad. Refill system as said start at bottom and work up. Check for leaks. Shutdown any call for heat. Open radiator valves and bleed rad. Check and adjusted system pressure where necessary. Run system and re-check. Inhibitor has been added without draining again.

    James.
     
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  8. dreadnoughtheating

    dreadnoughtheating

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    Has anyone mentioned what happens when a sealed system Boiler/Combi is drained?

    Either a) close iso valves to prevent draining the boiler/dragging air into it through auto air vents.

    b) do not worry about this, turnoff gas supply after refiling and power her up so pump spins&clears out air (hopefully? AAV's seem to have a habit of not opening/shutting as well as they do when new!), that way the burner will not fire and burn out your heat exchanger….

    Either way, be prepared for a whole of air to be shunted around the system.

    You may wish to consider fitting a magnetic filter while system is empty (my current choice is ADEY magna clean Pro), which can then double up as a dosing vessel for convenience when adding inhibitor.

    I do hope that is not too many trade 'secrets' divulged.

    DH
     
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  9. Whitling2k

    Whitling2k

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    Wow thanks you lot - there are some really good tips on there! should go into the FAQs!

    I'll definitely isolate the boiler until I'm all filled up, love the tip about locking the inhibitor into a drained radiator. I'll leave the mag-filter for now - part of my project is to remove a section of the network and leave it temporarily capped off with iso valves until I add the rest of updated network back in.

    I presume I can just add one in at that point?

    About to start - wish me luck!!
     
  10. Whitling2k

    Whitling2k

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    All done and seemed to go well! I was a bit aprehensive about this one - only seen one vented system part-drained before and that caused problems!

    I think kudos to the original installer of this heating system. The only minor niggles I had were with parts of the system that had been "user modified" in the past - mixture of compression and some cheapy second rate plastic push to fit had been used - but not properly. I managed to remove some plastic-to-compression fittings by bending the joint slightly!

    Anyway all thats gone now!

    The only mishap I had was spilling some x100 on the floor - I made a contraption out of a funnel bunged into some old damaged 15mm speedfit pipe, in-line compression joint and 1/2" tap extender - which worked well until the air lock forced a bubble up through the funnel!

    I removed the opposite blank plug et voila!

    Thanks again for your tips - they made (relatively!) easy work of it!
     
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