Hot water only comes on when two taps are used

Discussion in 'Plumbers' Talk' started by Serge373, Oct 2, 2020.

  1. Serge373

    Serge373 New Member

    Hello all,

    We have an Ideal Logic 35 Combi boiler (7 years old) and after changing the shower mixer and the kitchen tap, I am experiencing some issues with it.

    Both the shower and the kitchen tap, will, a lot of the times, fail to fire the boiler up. The shower mixer is a bit better, as in it would get the boiler fired for a few minutes but then would go 'ice' cold - that's when I need to turn the bathroom tap on, then both will get warm and stay warm. If I turn the bathroom tap off, the shower mixer will eventually get cold again in a few minutes. Leaving both on is a solution, but then the shower is quite weak - not the best way out.

    The kitchen tap situation is quite similar, except that it rarely fires the boiler up at all. I need to go into the downstairs loo, turn the hot water on there and then I get hot water in the kitchen - for a short time.

    I assume the new fixtures have slowed down the flow of water and the 'demand' is now not strong enough to 'wake' the boiler up - is that a fault of the fixtures, or should the boiler be able to handle that? The 'not hot' water flows at a pretty good rate, but probably not as strong as with the old fixtures.

    Was thinking of the diverter valve, after some googling, could that be it? Not a DIY job, I assume, unless I can spray some 'boiler WD40' to get it to move more freely or something of the sort?

    Any other suggestions appreciated, will probably be calling a plumber/heating engineer sooner rather than later as it is becoming a major inconvenience.

    Thanks,
    Serge
     
  2. terrymac

    terrymac Screwfix Select

    Measure the flow rate of water, from hot tap ,with tap fully on ( don't worry about what temperature it is )see how many litres it gives in 1 minute.
    Your boiler needs a minimum flow to trigger it into action.
    If the tap/ shower gives that flow and doesn't fire the boiler ,it's a boiler issue.
    If they do not give the minimum
    Flow then there is an issue with the supply to them , being restricted .
     
    Serge373 likes this.
  3. Serge373

    Serge373 New Member

    Thanks, terrymac, how would I find out what the minimum flow needed to trigger the boiler is? I have the Logic 35 instruction manual, do you know the official term for that?

    Just measured the water output from the kitchen tap - 4.6l/minute, while the old, working loo tap - 8.6l/min.

    Quite a difference!

    I've fitted isolation valves (these ones) when installing the new tap, as the old tap was 'hard-piped', could they be the problem? Should I try full-bore valves instead, like these?

    Thanks again!

    Serge
     
  4. terrymac

    terrymac Screwfix Select

    4.6 ltr/ per minute is a poor performance from the tap for sure. I assume there are flexible tap tails supplying that tap ,which are usually very small diameter internal bore and very restrictive , as are a lot of those isolation valves.
    However 4 litres per minute should certainly trigger the boiler into life ,you will need an engineer to investigate the boiler.
    You can do as you suggest and change isolation valves for full bore ,but more importantly check the supply hoses for kinks / sharp bends and partial restriction ,some have a gauze filter on the end that connects to the isolation valve,check that out too. The spout of the tap may also have a filter to check.
     
    Serge373 likes this.
  5. MGW

    MGW Screwfix Select

    I had same problem with mothers house, found a flexible hose had a slight kink in it.
     
    Serge373 likes this.
  6. Serge373

    Serge373 New Member

    Thanks again, ordered the full bore valves and will look out for kinks and bends while I'm there as well.

    I've checked the spout filter, made no difference with or without, so will look for other ones.

    Will update when finished, hopefully tomorrow, a visit from the engineer is probably in the books soon anyways, just wanna make sure it's not something minor that I can do myself before that.
     
  7. Serge373

    Serge373 New Member

    Thanks, I'll install the full bore valves and inspect the hoses, they did seem very narrow compared to the original pipes, but hopefully they will do a good enough job with the larger valves! Fingers crossed!
     
  8. Serge373

    Serge373 New Member

    Apologies for disappearing for a while, been a busy week!

    Finally got to change the isolation valve to a full bore one,but unfortunately it had zero impact on the boiler firing! I measured the flow from the kitchen tap again and it stayed at 4.6 l/min, so I guess it wasn't that.

    This is the diameter of the flex hose that feeds the tap - I guess this is where the flow gets restricted, or maybe inside the tap -

    [​IMG]

    So, what are my options now? Should I try a different, higher flow tap? Is there such a thing? Or is it time for a Heating Engineer, as the boiler should kick in at that flow rate regardless?

    Thanks in advance,

    Serge
     
  9. terrymac

    terrymac Screwfix Select

    How many litres per minute does the cold run from kitchen tap ?
     
  10. Mike83

    Mike83 Screwfix Select

    If your exceeding the minimum flow rate by at least a litre it should fire.
    Could maybe be an issue with the turbine or flow restrictor.
     
  11. Serge373

    Serge373 New Member

    4.6 l/min as well! I guess that's the most the tap can deliver then? Is that sub-par?
     
  12. Serge373

    Serge373 New Member

    How do I find out what the minimum is?
     
  13. Mike83

    Mike83 Screwfix Select

    Minimum is about 2lpm.
    4.5 should fire it.
     
  14. terrymac

    terrymac Screwfix Select

    That's ridiculously low for mains pressure. When you changed tap and shower valve ,what isolators did you use ? Are they fully open ?
    From memory the boiler needs around 3 LTRs/ mins to fire up, may be wrong there.
    Seems like you have two issues ,boiler and a rubbish tap.
    I would be interested to know ,if, you remove the Flexi tap tail from the isolation valve and rig up a makeshift bit of 15mm copper pipe to the isolation valve, directed to a bucket, and see what flow is coming from the isolation valve . If its twice or more than tap ,change the tap !!
     
  15. Serge373

    Serge373 New Member

    The shower mixer is smaller, physically, and I remember it advertised a 'water saving feature', which I think just means low flow. I did notice a significant drop in pressure when I first went for a shower with the new mixer, but there were no issues with the water getting cold. I didn't set up any isolation valves for it, just screwed it right on.

    For the kitchen tap, I have just installed a full bore 15mm valve today, and checked for kinks, but the flow is still the same - it must be the tap's maximum, which is just not enough to trigger the boiler - so yes, it's probably both!

    Both the cold and hot flow from the kitchen tap are plenty sufficient for everyday tasks, it's just that the boiler is not firing!

    I don't have any spare pipe or the skills/experience to create a rig as described, but I imagine the water flow would be about double, similar to the one from the toilet tap, if I was to direct it into a bucket.

    I will probably go ahead and get an engineer to look at the boiler - we were planning on changing the taps in the rest of the house, eventually, and would need a properly working boiler. I can always get a 'high flow' tap and swap it myself, if needed.

    How much do you reckon a new turbine and/or flow restrictor would cost, labour n all?

    Thanks,

    Serge
     
  16. terrymac

    terrymac Screwfix Select

    Ok ,if your happy to accept the flow from tap just get the boiler sorted ,Go for a fixed price repair . As example ,from BG £250 ish ( more if in London)
     
    Serge373 likes this.
  17. Mike83

    Mike83 Screwfix Select

    It may just be debris in the flow restrictor.
    Could be a simple fix.
     
  18. terrymac

    terrymac Screwfix Select

    Doubt it Mike ,wouldn't get 8 LTRs / min from other hot taps.
     
  19. Serge373

    Serge373 New Member

    Hello everyone,

    sorry to leave it so late, only managed to get the engineer in this last Sunday and the forum was down then.

    The Scottish Gas lad came in, went straight for the Hall sensor and the flow turbine - he said the sensor was 'clicking' on and off, so he took out the turbine and luckily had a spare one in his van. Fifteen minutes later the new turbine was in place, the sensor stopped 'clicking', and all has been smooth sailing for 3 days now. He also ran a few more tests, said everything looks good and left within 1 hour of entering the house!

    Easy peasy, only cost me the insurance excess of £99 - how much would a call-out engineer charge for similar work?

    Thanks again for all your input, will update again if situation develops again (fingers crossed - it doesn't!)

    Cheers, what a helpful place this forum, I'm now a regular reader!
     
    terrymac likes this.
  20. terrymac

    terrymac Screwfix Select

    Thanks for letting us know ,glad your sorted .
     

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