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New Glow Worm Combi Low Flow Rate

Discussion in 'Plumbing and Central Heating' started by rideforever, 5 Jun 2020.

  1. rideforever

    rideforever

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    Hi. Just had a 30kw Glow Worm Ultimate installed producing 10l/min of hot measured at the kitchen tap, with cold of about 19l/min.

    Previously had a 18 year old Xtramax producing 14.5 l/min of hot even though the storage on the Xtramax didn't work any more.

    The Ultimate is rated 12.4 l/min, the previous Xtramax rated 11.4 l/min.

    Is there a problem and what kind of problem could there be ? Cheers.
     
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  3. Gasguru

    Gasguru

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    Are you saying with the tap fully open the maximum flowrate from the tap is now only 10l/min?
     
  4. rideforever

    rideforever

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    Here's a photo of cold and hot out the tap. Tap is 3 ms from the boiler on the other side of the room. It was about 14.5l/min for the Xtramax measured about 6 months before its removal.


    ch2.jpg
     
    Last edited: 5 Jun 2020
  5. Gasguru

    Gasguru

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    Remember the specification will be 12.5 l/m raised by a particular temperature..normally 35 degrees so that's around 12 litres/min of hand hot water and considerably lower flowrate at 60 degrees.
    most boilers have a flow limiter to stop customers complaining of poor hot water performance if they open the taps too much (especially those on high pressures).
    I wonder if you have poor supply pressure...are the other taps just the same.
     
  6. rideforever

    rideforever

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    Thanks. I don't really know what that means, if I turn the tap so some cold is added to the hot then the rate goes up to about 12, but of course now you have the mains pressure added to it so the boiler can't take credit for it.

    The fact is in the specs it says 12.4 l/min. The old boiler specs said 11.4 l/min.
    But the result at the tap is about 1/3 less pressure on the shower and hot water at the tap.
    So I am pretty f***ed off. Especially since for about £80 more I could have had the 35kw boiler.
    But I got the 30kw because my last boiler was also glow worm and 28kw.
    So I basically bought a boiler that is spec'ed higher than the last one, is 20 years newer but has 1/3 less real world performance.
    So I will have **** showers for the next 20 years or spend another £2000 on it.
    Should I not be f***ed off ?

    I know Glow Worm has been taken over by Vaillant, I don't know if that means they are a s*** company now.
     
  7. oldbuffer

    oldbuffer

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    1. There is no way of telling if your pressure and flow rate now is what they were six months ago when you measured the flow rate of the old boiler.
    2. You need to know the pressure (static and dynamic) of your incoming mains water, together with its flow rate.
    3. The pressure and flow rates may well vary at different times of the day, depending on local usage. So measure, if possible, at 08:00, 13:00 and 18:00 for a few weekdays and a weekend or two.
    4. As Gasguru said, a combination boiler can heat a certain amount of water at a time.
    4a. For your new boiler, a 12.4 litre per minute (lpm) flow of hot water is the highest flow which can be heated from the temperature of the incoming cold water to a temperature 35 degrees hotter than that cold water.
    4b. So, if the incoming cold is at 10 degrees, you will only get 12.4 lpm at 10 + 35 = 45 degrees.
    4c. If the flow is higher, the output temperature will be lower.
    4d. If the flow is lower, the output temperature will be higher.
     
  8. Gasguru

    Gasguru

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    I've just had a look at the manual for the Ultimate 3....
    As you point out the 30 kW will raise the water temperature by 35 degrees at a flowrate of 12.4 litres/min and the slightly more powerful 35 kW will raise
    the temperature by 35 degrees at 14.4 litres/min. This is basic physics and is common to all boilers (the calcs are very simple). Increase the flowrate and the temperature rise is lower and vice versa.

    If customers were to open a hot tap too much, or if they have excessive water pressure, or perhaps they have an old 3/4 bore tap the resulting excessive flowrate may not achieve the desired temperature...especially in Winter time when the incoming cold temp is very low. It is therefore normal for boiler manufacturers to fit a flow limiter to help prevent this scenario (and reduce calls to the customer services hotline).

    Looking at the boiler spec for some reason Glowworn have decided to fit a 10 litre/min flow limiter to your model. Now even in Winter when the incoming temp may only be 5 degrees a 12.4 litres/min flowrate will result in a 40 degree outlet temperature which for many would be adequate for bathing etc. Certainloy

    This boiler model is also sold under several other model names from Vaillant. For the same kW rating some have the 10 litre/min flow limiter and some have the 12 litre/min.
    I can't see any logical reason for fitting such a low output flow limiter other than either a mistake or to fiddle to efficiency figures.

    From the parts diagram the flow limiter (it's just a plastic disc containing an o ring) appears to be in the screwed connection between the boiler hot outlet and the elbow fitting.
    Removal of the O ring is normally sufficient to circumvent the flow limiting.
     
  9. rideforever

    rideforever

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    thanks
     
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  11. rideforever

    rideforever

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    Is it legal to sell a boiler with an advertised flow rate of 12.4l/min but have a rate limiter of 10l/min.
    Isn't that simply fraud, the specs are not true, you are actually selling a boiler with a lower output then advertised ???
    It's like saying your car does 0-60 in 5 seconds and it ends up being 8 seconds.
    That's fraud.
    On Monday the limiter will be removed, I have no idea what will happen then, but as it is currently produced just under 10l/min ... I can only assume ... well I have no idea really.
     
  12. ScottishGasMan

    ScottishGasMan

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    Firstly there is no advertising that says it will give you what you say, all boilers must state a flow rate at a given temperature rise regardless of what the set flow rate is. eg the extramax will state 11.4l/min at 35 degree rise

    secondly, as above there is a 10l/min restrictor fitted so in terms of design it would appear that your boiler is working exactly as its meant to.

    This is something that should have been discussed between yourself and the registered gas installer fitting the boiler.

    You could ask the installer to remove the restrictor, you will achieve higher flow rates, but at a lower temperature rise, same as any combi boiler.
     
  13. Gasguru

    Gasguru

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    The issue is that Glowworm have fitted an unecessarly low flowrate limiter...look at comparable 30kW boilers and they are normally 12 litres/min. Look at the Vaillant badged versions...12 litre/min.
    Do the maths and there's no logical reason for such a low flowrate.

    Take it to an extreme and let's say they fitted a 5 litre/min flow limiter. Sure you could fill the bath at 60 degrees and add cold to give you a decent bath fill flowrate but where's the sense in heating up the hot water so much only to cool it back down to a bathing temp.
     
  14. rideforever

    rideforever

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    On the Glow Worm website for the "Ultimate" (the most expensive of their 5 combis) it says 12.4 l/min. But due to the restrictor it actually produced 10l/min. I think that is defacto fraud as is deceives the capabilities of the boiler.
    What more to say.

    If you advertise a car as 150mph top speed, and customers get a car that does 130mph top speed ... that is fraud. Period. If that's not fraud what else is?

    I have no idea why that restrictor is on there, perhaps it's bad news and removing it will cause follow up problems ... i.e. during production they recognzied a problem with the machine and bodged it to conceal the problem.

    Or perhaps there is some reason they wish to have higher efficiency ratings maybe for the EU or because greeeniecustomers demand it, or maybe its just an admin error or other bureaucratic reason, or the supplier of the boiler had those going to Kazahkstan which get the limiter. Who bloody knows.

    Maybe it gets taken off and 12.4l/min comes out the boiler it's all forgotten. I am not using max temp in the shower anyway, the temp handle is about half way.

    Moreover in terms of comparing Glow Worm products, the 11.4l/min 28kw unit seems to produce more than the 12.4l/min 30kw unit ... so what are you supposed to do ... guess ?
    How else do people compare or estimate the amount of hot that comes out ... I had several installers in here to quote ... they are all using that figure.

    Anyway we'll see. Luckily the shower is bearable even as it is, i.e. we can still wash ourselves under it !!!
    Too much washing is not good for the immune system, and frankly 3 weeks of buckets showers have got me used to it, and wearing jumpers.
     
  15. Gasguru

    Gasguru

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    Once upon a time when boilers were built with quality they would often have an adjustable flow valve built into the water sections in order to limit excessive flowrates...then the accountants stuck their
    beaks in and now all boilers have a 2 penny plastic insert. As I said it is normal to remove the flow limiters where pressures are low or the flow limiter O ring has gone solid and is restricting the flowrate.

    Glowworm are one of the worst manufacturers for serious mistakes in their manuals....more so than anyone else.

    It's probably a result of the considerable re-badging Vaillant group do. Not sure of the current range but some Glowworms have been Turkish Heatlines underneath....
     
  16. rideforever

    rideforever

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    Perhaps you can advise me. The installer has spoken to GlowWorm and they said the flow limiter cannot be removed or it invalidates the 10yr warranty.
    I will have to speak to them myself.
    I am starting to think it's time to claim the price of the boiler at the small claims court for fraud.
    It's patently not a 12.4l/min boiler and that advertising that all installers are using is a fraud.
    Just checked the manuals the other combis they have.

    ULTIMATE : Restrictor
    STORE : no
    ENERGY : no
    BETACOM : no

    So it seems that the advertised value is reliable for Glow Worm products, but on the Ultimate they have for whatever reason created a situation where they advertise 12.4l/min but only deliver 10l/min.
    That seems like de factor fraud.

    And actually the 10year guarantee on this boiler ... seems to be a fiddle based on running your machine at a rate comparable to a cheap machine.
     
    Last edited: 15 Jun 2020
  17. denso13

    denso13

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    Fraud is a police matter. Give them a call and let us know how you get on.
     
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