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Cold upstairs radiators needing constant bleeding

Discussion in 'Plumbing and Central Heating' started by bfmonaghan, 17 Nov 2010.

  1. bfmonaghan

    bfmonaghan

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    Hi all

    Have used this forum a lot over the past year, but this is the first time I've a problem that I can't solve.

    I recently bought a house that has a recently installed (1-2 years ago) central heating system. Whiel the downstairs radiators work fine and are hot from top to bottom, I've real problems with the upstairs radiators. They all appear to fill up with enormous amounts of air and are cold except from the very bottom of the radiators. Bleeding the radiators takes forever, as the air doesn't appear to be pushed out under any pressure. So I have to open and close the valves on each to coax the air out. When I do get water coming out, the radiators are hot - but within a couple of weeks, they have filled with air again.

    I've looked at the header tank which was filled with dirty water and a lot of debris which had covered the sides of the tank and the float (rigth term?). It looked like the vent pipe was also under the water level. So I baled that out - horrible job - and it has refilled to a good level (over outlet, but under vents).

    Next thing I was going to try was to balance the radiators to see if I can increase the pressure in the upstairs radiators so that I can get them to bleed more rapidly.

    But I'm not sure whether this is just a balancing issue, or whether something more fundamental is wrong and is drawing air into the system.

    Any thoughts or suggestions would be appreciatted.

    B
     
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  3. 45yearsagasman

    45yearsagasman

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    I don't think rad balancing is the issue,but more likely to be cold feed/open vent blockage and system possibly pumping over.Feed/vent connections should be just upstream of pump.Taking ages to vent rads would be signs of a blocked cold feed.Venting with system off is important.
    Have you checked that it is air and not hydrogen?.Even though its 2 yrs old blockages can easily hapen in a short time.
     
  4. bfmonaghan

    bfmonaghan

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    Hi Thanks for really quick response.

    Have collected air from bleeding radiators in an upturned jam jar and stuck a match in - no pop. Just burns in the upturned jar.

    I check the cold feed at teh bottom of the header tank by sticking a srewdriver into the opening. No resistance and no debris - so looks like, at least for the first few inches, that there isn't a blockage.

    Only baled out the header tank last night and got the vent above water. I suspect that it was below water because of the debris that had accumulated on the float, which was pulling it down. I think that I might raise the float lelve though - by rotating it to make it longer - and reduce the water level in the header tank - that should give a greate rclearance between the vent and the water level.

    Haven't been near the pump. Shall look a t feed and vent connections tonight - from memory, I think that they are by the pump - but not sure if upstream or downstream.

    Any further thoughts appreciated.
     
  5. D_Hailsham

    D_Hailsham

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    The level should be above the outlet just enough so the float valve opens before the water level drops and lets air down the outlet. You adjust the level, when the heating system is cold, by bending the arm of the float valve.

    Bleeding should be done with the system off and the water cold. Bleed downstairs rads first. Set the motorized valves to MAN while bleeding.

    Is there an air valve on the feed pipe from motorized valve to the HW cylinder?
     
  6. 45yearsagasman

    45yearsagasman

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    You will find the cold feed connection on the suction side of the pump.Depending on configuration it will be 15mm.Where it joins the system is where to look for blockage.Be prepared to lose a little water.The cold feed may have a gate valve to isolate if not then tying up the ball valve or bunging the cold feed outlet in the f/e tank will do.
     
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  7. bfmonaghan

    bfmonaghan

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    Thanks for that.

    SO level in header tank was way higher than just above outlet. Even after baling out, it still is quite high - 6 inches say - but at least below the vent opening. So shall bend float arm and bail out again to get the water level down further.

    Have been bleeding system with system on and water hot :oops: Will get this rigth next time.

    Next bits are testing my capabilities though. Not sure what's meant by the motorised valves and settign to manual - could you explain.

    Re the HW cylinder - we've a grants oil fired outdoor boiler with 2 sets of feed and return pipes. One set goes to the HW cylinder and the other set has the pump, feed to the radiators and the piping to the header tank. At least that's how it appears to me. So I thnik that the CH and HW systems are independent - although I can't have the CH on without the HW also being on. But always a possibility that I have this wrong!!
     
  8. D_Hailsham

    D_Hailsham

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    You have a gravity HW, pumped heating system. So forget what I said about motorized valves. You won't have any with your system.

    This type of system is not very efficient and is no longer allowed for new installations or if you are replacing your boiler. It might be worthwhile getting it updated to a fully pumped system.
     
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  9. bfmonaghan

    bfmonaghan

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    I was thinking of replacing the HW tank, since it's only 140 litres and is poistioned a bit inconveniently. Would I be able to change to a fully pumped system with my existing boiler? I think that it's decent quality and only a couple of years old - so I'm not keen to replace just yet.

    But the system design isn't an issue for my current problem with the radiators though, is it?
     
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  11. bfmonaghan

    bfmonaghan

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    Thanks 45yearsagasman

    May be a dumb question - but how do I check for blockages where the cold feed joins the system. Do I have to open the pipes up? I think all the connections are rigid and fixed - so I'll need a plumber for that?
     
  12. D_Hailsham

    D_Hailsham

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    I'm surprised it wasn't converted to fully pumped when you had the boiler installed - the regulations were in place then. Ask your installer when getting a quote for the new HW cylinder. Apart from pipework alterations you will require one or two motorized valves, a cylinder thermostat, a wiring centre (junction box) and a new programmer or programmable thermostat.

    Agreed, it was a diversion ;)

    Set the level (but not too low) and bleed the rads as I suggested. Then report back what happens.
     
  13. bfmonaghan

    bfmonaghan

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    Thanks - shall see how I get on this evening.
     
  14. bfmonaghan

    bfmonaghan

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    Thanks for all assistance yesterday.

    Bled radiators again last night - with system off and cool. And rads bled quickly, so looks like my initial problem of not getting them to bleed was because I had the system running. :oops:

    Looked for where cold feed from f&e tank joins the system, and it's not near the pump. I couldn't actually find the join, so it must be underneath a floorboard or behind a wall in an upstairs bedroom. Will be an issue if I do have to get at it!

    I found a 5l empty bottle of Sentinel X500 beside the f&e tank in the attic, and wouldn't mind some advice on whether I should add something similar to the f&e tank, given that I bailed it all out. I think that I should be able to just add the X500 into the f&e tank - but am not 100% sure that's ok and also not sure of how much to add. Any views would be appreciated.

    Thanks
     
  15. D_Hailsham

    D_Hailsham

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    Here endeth the first lesson. ;)

    Can you find where the vent pipe joins the flow from boiler to pump? The vent should be about six inches away, nearer the pump.

    If you can only find one pipe (22mm) the system may have a combined feed and vent. In this the 15mm feed pipe connects into the vent pipe before the vent joins the flow.

    Also, as you have a gravity HW/pumped CH system, the feed and vent pipes may connect into one of the flow or return pipes near the boiler.

    X500 is a combined inhibitor and antifreeze. Not often used, unless the installation is prone to freezing up. In any case there are other ways of preventing the system freezing up - insulating exposed pipes, frost thermostats etc. Is your boiler in an unheated boiler house?

    Whichever product you use, just pouring it into the F/E tank is pointless. It has to get into the system to do any good. This means: draining down until the level is just above the outlet; adding the inhibitor; draining down so the inhibitor enters the system; filling the F/E tank to the correct level.

    There should be a drain outlet on a radiator or near the boiler.
     
  16. bfmonaghan

    bfmonaghan

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    Thanks again for your help.

    The feed and vent joins to the main system are really testing me. What I think I have is:
    1. On the ground floor, 2 22mm pipes (the ch set) from the boiler into an airing cupboard. There's a pump and another unit (an actuator, think) on the pipes and they run vertically into the attic above the cupboard.
    2. In the attic, the 2 pipes each have one t junction, each of which connects to the white piping that feeds the radiators. The 2 white pipes then disappear under floorboards in the attic. The 2 22mm pipes then head horizontally through a stone wall into the floor area below a first floor bedroom.
    3. In the main attic (above the first floor bedroom), I have the f&e tank. A single vent pipe comes through the floor of the attic (ceiling of the first floor bedroom) and stops above the f&e tank. The cold feed from the f&e tank also disappears down the same hole in the attic floor.

    So, I can't actually see where the pipes from the f&e tank in the attic join the 22mm pipes from the boiler. So, it looks like it must happen somewhere in teh walls or floor of the first floor bedroom. If I'm right, tehn these joins are happening quite a distance from the boiler or the pump.

    For completeness, there is another vent pipe that comes up through the attic floor and stops above the cold water tank. I'd thought that must be the vent from the hw tank.

    Does that make any more sense?

    Re the draining down, I haven't found the drain cock yet, so will have a hunt around to see if I can locate it tonight. Thanks again for your help.

    B
     
  17. D_Hailsham

    D_Hailsham

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    This is where online diagnostics become almost impossible.

    Try tapping the feed and vent pipes with a hammer and see if you can feel the vibrations anywhere else. It's crude, but may work

    Can you post a pic of the "actuator" near the pump? Or info about make and model no etc?

    That only accounts for two of the three connections to each T-junction

    That's correct.

    If its not on the last rad in the system, it's probably close to the boiler.
     
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