radiator not getting hot water....but I've tried just about everything..help....

Discussion in 'Plumbers' Talk' started by every day is a school day, Nov 20, 2021.

  1. dcox

    dcox Screwfix Select

    OP said it had worked for a few months after new pipes put it.
    exbg likes this.
  2. Teki

    Teki Screwfix Select

  3. exbg

    exbg Active Member

    Sorry, Mac, but I know from bitter experience that, eg, a nail in a pipe will present a great enough resistance to FLOW kill the rad, but would still pis$ out of rad valve if disconnected. A rad connected to a drain cock outlet would be unlikeley to work, but the DC obviously passes a lot of water (well, some of the time ;)) if opened.
  4. So to respond LOL

    My home is a one off, designed by architect and built by a local stone mason. It is big by regular detached 5 bedroom standards... but not a mansion...

    So the flow might be restricted rather than blocked. You can determine "blocked" but not "restricted" so nothing there to use. Flow can be measured easily just as you would any tap, the question is once again, what does the radiator need to function? 20 litres per minute? 40, 60?

    The rad stopped working between say April and late October. It worked in last heating season, its not working now.

    What constitutes as restriction? a reduction in water flow in this case, so once again, what flow does it need to be because I'm sure a bucket and clock can determine this

    The overall system now has 3 air vents (one at the boiler I'm told and 1 in the middle and another which is the very first (or last) radiator which has one of the auto bleed vents in it

    There is only one non return valve which he said was more to eliminate a possible cause. Are you saying that having this in place is actually creating more of a problem?

    Kink agreed, that would restrict flow so again, how do I know what the flow should be so I can measure this

    Nail in a pipe..would I not have a leaking system losing pressure? I'm sure I would. A nail through a pipe without a leak?

    Random valve? what does that mean?

    If they have left the micro bore then its around 6m (12m) in total. To counteract that, there is a connection to a landing radiator that comes through the wall of the garage (so around 12m long (24m return)) and that radiator is probably the warmest in the property. In any event, the property was serviced by mirco bore when it was commissioned and it worked just fine.

    So my take away question for you is once again, what flow rate should the radiator have so I can go and measure this and get an answer. If you can give me that value I can either eliminate or home in.
  5. Kas228

    Kas228 Screwfix Select

    Is there ANY heat at all in the radiator (sorry if mentioned previously), is it stone cold to the touch, ie getting zero flow through it?
  6. Mike83

    Mike83 Screwfix Select

    Earlier I mentioned 1lpm for a standard radiator. This would be sufficient on a system that’s working correctly.
  7. dcox

    dcox Screwfix Select

    Mike suggested 1 litre per minute earlier would be enough to heat the rad. I’d expect perhaps 10 to 20 litres per minute from an open pipe if the system pressure was around 1 bar.
  8. Mike83

    Mike83 Screwfix Select

    I would expect a fully open lockshield valve with constant pressure to also flow at 10-20 lpm depending on the mains flow in to the property.
    A radiator once balanced will run at 1lpm or less.
    But if your only getting 1lpm at the valve you’ve got an issue.
    If you’ve got 10lpm plus at each valve then it doesn’t seem blocked but one pipe will be pushing in the opposite direction from normal.
  9. exbg

    exbg Active Member

    Bizzarely, it is possible for a nail in a pipe to be "sound". If it is not in a high traffic area, and not subject to movement, it may never leak. You will notice it when you pull the nail out. To be fair, a leak is more likely on a combi than a tank fed system.

    You cannot measure "flow" in that sense. You can easily disconnect the valve, and measure the "flow" in terms of litres per minute, but that is completely different to flow in an enclosed circuit. When properly designing, and pipe sizing, a system we look at "resistances", influenced by pipe bores, length and bends. In practice, though, I would say most domestic systems are "designed" by rule of thumb and experience.

    The NRV will not necessarily be causing a problem, but will definitely be adding to the resistance (simple physics) and should not be there. It could even be faulty, although the issue was there before it was fitted. You also say that it is definitely on the return, but you are relying on a label, which you have no guarantee is correct. Any of us here could easily work out if it is the return, so presumably your plumber was able to check, and did.

    In truth, it is all a little academic. There is a physical problem, the problem has occurred after the installation, so is an evolved issue, not a design one. You, therefore, have to consider what may have changed. A straight section of pipe has eliminated the rad being a problem, you have said the problem has occurred with 3 different sets of valves. That clearly leaves the pipework at issue.

    Is it possible to access the pipework, or do you have laminate etc?

    Re the MB: is the garage a separate circuit? MB itself is not a problem, other than ot is more easily blocked or physically damaged (kinked). Would the MB have been left in due to difficult access?
  10. In which case the TRV side is like that but a lot slower on the return pipe at the point it joins the main return pipe. So any "restriction" is on the return pipe then.
  11. 1 litre per minute? so a very low trickle...the flow would easily by 10 litres per minute. so my plumber was correct in fitting the non return valve to counteract this pushing from the opposite direction.
  12. exbg

    exbg Active Member

    Bizzarely, it is possible for a nail in a pipe to be "sound". If it is not in a high traffic area, and not subject to movement, it may never leak. You will notice it when you pull the nail out

    You cannot measure "flow" in that sense. You can easily disconnect the valve, and measure the "flow" in terms of litres per minute, but that is completely different to flow in an enclosed circuit.
  13. Mike83

    Mike83 Screwfix Select

    There will be no pushing from the opposite direction when a system is running. So a NRV isn’t required.
    When I say 1lpm this means the radiator is maybe passing 1lpm when running. This is set at the lock shield valve usually.
    If it’s easy enough to get under the floor and remedy then go for that.
    If the system is piped correctly then there’s ways to tell what pipe from the flow and return is causing the issue. But even knowing this doesn’t solve the issue.
    dcox likes this.
  14. dcox

    dcox Screwfix Select

    Until the rad is warming up (when you’d be able to feel which side gets hot first) it’s best not to assume which is flow and which is return, even though they’re labelled.

    To clarify what you said about different flows from each side: if you closed the valves and took the new rad off then opened each valve one at a time into a bucket, you’re getting much more flow from the Trv than the lockshield (with the lockshield fully opened)? If so, then yes, you could assume there is a restriction on that pipe to/from the lockshield.
  15. I had an engineer friend design my system and he gave the drawings to a local plumber to fit them. I would say I have around 35-40% less pipework as it was laid in the shortest runs and removed the totally unnecessary twists and turns.

    All of the basins and toilets have a small diameter pipe to them and he changed the way the cold water is distributed around the home so the boilers always have the priority feed. His ideas worked as I don't get a huge deluge when turning on a small basin tap and you can turn on any tap in the house and flush toilets and it never effects the shower flow...I hated that with the old combi.

    Not only labels (I asked for everything to be marked for future reference) but also the pipes were marked as to their destination and if they are flow or return. So unless the whole thing is inverted (flow is return and return is flow) I know for certain. (but now you have made me think)

    The new pipework has been placed where it can be accessed for inspection apart from the bathroom floors which are tiled. I'm lucky in that on the lower floors, there is access through inspection hatches. He designed it so that I can isolate any radiator or tap without switch off the water or draining the system.
    The micro bore section in question is the only length that was cut into a wall when the property was built (which is why they said the plumbers were the last one's in when it was built) so its impossible to get to. This is on my list of jobs to have done i.e. re-route this pipe so it is accessible.
    That brings me to another distinction...this radiator is the only radiator where the pipe travels upward from the main pipe where the other radiators on this floor are all horizontal runs. Could that be something? In saying that, the flow is fine so this upward rise can't be having an effect

    Every radiator has its own circuit i.e. a pipe coming off the main pipe and back to the main return. No radiators feed other radiators (so I'm told) where the old system had micro bore feeding other micro bore feeding radiators. I'm wondering how it even worked.
    exbg likes this.
  16. pppmacca43

    pppmacca43 Super Member

    I don’t disagree:)
    I was just saying that the OP had confirmed the radiator had worked since the works were carried out.

    TBH I don’t think the OP will get an answer here, like has been said somewhere above it must be a blockage or restriction, air, or a pump issue. It really needs another plumber on site to investigate further. It sounds like one we had at work recently as I explained before where I did all the usual stuff such as balancing, shutting off all other rads, taking radiator off and blasting through valves full bore for ages etc and hoping for a big glut of air that never came lol, and to my surprise ended up being the pump in the combi boiler not performing properly despite spinning. The rad was in a hallway on a middle floor but must have had a long run from somewhere and the pump just wasn’t getting it round that radiator. This probably isn’t the same and most of the time it’s a restriction or blockage but I wouldn’t rule it out as I previously did.
    exbg likes this.
  17. dcox

    dcox Screwfix Select

    If every rad can be isolated it’s possible that the isolation valve hasn’t properly reopened. Even if the handle looks to be in the open position sometimes the valve itself isn’t.

    If this one radiator has some vertical pipework looping down to it then an airlock is more likely than on horizontal pipework.
  18. exbg

    exbg Active Member

    Good point about the valve!
    OP: is it a lever valve or a gate valve (round, red normally, wheel head to turn)?
  19. exbg

    exbg Active Member

    Yes, that was my first thought on reading that response. Can’t really visualise thx set up, though
  20. One thing I have noticed this last week, perhaps someone can explain. The heating pressure gauge was raised from 1 to 2.5 in an attempt to force any trapped air he said. I have noticed that the radiators are cooler at the same set temperature with this high pressure. Is that a thing or my imagination?

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