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Thread: Hot water woes - any engineers?

  1. #1
    Craftsman Gromdal's Avatar
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    Hot water woes - any engineers?

    I've had three heating engineers out whenever this issue presents under my emergency homecare package and not one of them has been able to adequately resolve a recurring issue and it's starting to wear thin so I wonder if the collective has any thoughts because I've drawn nothing but blanks.

    We have a Glow Worm Flexicom 18sx condensing boiler, a Drayton Lifestyle programmer for hot water and upstairs central heating and the downstairs underfloor is controlled by Heatmiser programmable thermostats across 4 zones. I also have a solar thermal water system on the roof connected to the water tank. The heating works perfectly every time we ask it to. The hot water works all the time within it's timer settings UNLESS the tank has drained itself of hot water, which means that after a bath and a heavy washing up session have exhausted the tank, trying to manually advance the hot water or set to always on results in nothing happening at the boiler, or the diverter valve if the heating is already on. If you reset the thermostat on the tank, the diverter will spin up and send a pulse of hot water to the tank if the central heating is on and then stop, even if the programmer is set to on rather than timed. Nothing I did last night would allow hot water to be pushed to the tank, boiler reset/thermostat reset/triggering all the heating zones etc. The diverter was replaced the first call out, the thermostat identifed as potentially faulty second call out so I was shown how to reset it and the third call out was for a replacement expansion vessel on the boiler but when asked about the hot water they were also at a loss to explain. I don't actually know how hot water was restored the first two times by the engineers.

    Here's where it gets stupid - this all happened again last night, and I gave up and went to bed destined for a cold shower this morning. I woke up and the boiler had triggered the heating upstairs correctly at half six, and had also heated the hot water tank from it's overnight low of 17c (my solar thermal water system has two probes so I can see what the tank temp is at two places) back up to where it should have been at 65c. I have absolutely no way of accounting for why this is happening. The hot water period between 0730 and 900 has now finished this morning, and if I go and advance the hot water (having fed two showers and it reading 57c) the boiler kicks in as if nothing happened and starts delivering hot water to the tank.

    Now, we mostly get round this by just not using all the hot water, but this is pretty unsustainable going forward because we don't have any backup electric shower or a working immersion (I press the switch and nothing happens?), so when we lose hot water on demand we seem to just have to wait for the next timed slot to kick in. I haven't tried removing the time slots from the programmer to confirm yet, but you'd have thought it would just be as simple as pressing the advance or setting to always on and it'd just...work?
    Last edited by Gromdal; 5th December 2022 at 12:58.

  2. #2
    Master
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    Some motorised valves in this set up? Are you able to access them?

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    Craftsman Gromdal's Avatar
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    Quote Originally Posted by MCFastybloke View Post
    Some motorised valves in this set up? Are you able to access them?
    Yes, in the upstairs airing cupboard - the left one was replaced 18 months ago, picture here: https://imgur.com/7NCEaLI

  4. #4
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    Does sound like a dodgy diverter value to me. Did they definitely replace it, or just manually trigger it a few times until it appeared to be operating normally again?

    Edited to add Iím most certainly not a heating engineer, but am used to replacing (and occasionally repairing) these God-awful valves!

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    Craftsman Gromdal's Avatar
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    Quote Originally Posted by Peck View Post
    Does sound like a dodgy diverter value to me. Did they definitely replace it, or just manually trigger it a few times until it appeared to be operating normally again?

    Edited to add Iím most certainly not a heating engineer, but am used to replacing (and occasionally repairing) these God-awful valves!
    It was a full replacement, the chap mentioned that they only seem to have a finite lifespan. I'd only been in the house for 3 weeks when they came out and swapped it and it was only 7 years old. I'd be inclined to agree normally but I can't get my head round why it works all the time except when the tank is stone cold, which is why a thermostat fault was also mooted but given that it came on fine this morning in the timer period and was the exact same temperature in the tank as it was last night I'm not so sure! I wondered if there was an issue with the silver box on the left of the picture as this is where the hot water sits below until the hot water tank asks for it at which point it flows up but this is independent of the motorised valves below?

  6. #6
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    Quote Originally Posted by Gromdal View Post
    Yes, in the upstairs airing cupboard - the left one was replaced 18 months ago, picture here: https://imgur.com/7NCEaLI

    Need to verify the valves are working right, when i had a similar situation it was one of the valves, firsts was the head, simple sniff test then remove the head showed it was burned out,second head cycled but valve seized.

  7. #7
    Master blackal's Avatar
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    A strange set of symptoms.

    1) Can you identify what the 'tank reset' is? Normally for a wet HW heating system you don't need a thermostat reset (I don't think). You do - on an an electrical element stat though.

    2) Simple thing today - is to swap around the motor-valves "heads" betwen HW and CH duty - there should be enough cable there to do that without any faff. BUT - isolate the electrical supplies to the valves, as you will have the cover off the head.

    Then - see how the system operates with the HW control doing the CH and vice versa.

    That should give a fuller picture.

    (if you do have a multi-meter, and are comfortable in its use - leave the head covers off and when you re-energise and signals are fed from the controller to the valve heads - you can check that the signal is getting through.)

    That's as much as I would guess at until you clarify those points.

  8. #8
    Yes - I would unclip the motor and see the the valve inside turns freely although if it does not sure how much that helps.

    Can't you just add more on/off cycles to the DHW programmer so it is on most of the time - give it less chance of the tank being emptied during an "off" period ?

  9. #9
    Craftsman Gromdal's Avatar
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    Quote Originally Posted by MB2 View Post
    Can't you just add more on/off cycles to the DHW programmer so it is on most of the time - give it less chance of the tank being emptied during an "off" period ?
    This is a very good point, because the culprit is almost always my wife's 9pm bath!

  10. #10
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    Quote Originally Posted by Gromdal View Post
    It was a full replacement, the chap mentioned that they only seem to have a finite lifespan. I'd only been in the house for 3 weeks when they came out and swapped it and it was only 7 years old. I'd be inclined to agree normally but I can't get my head round why it works all the time except when the tank is stone cold, which is why a thermostat fault was also mooted but given that it came on fine this morning in the timer period and was the exact same temperature in the tank as it was last night I'm not so sure! I wondered if there was an issue with the silver box on the left of the picture as this is where the hot water sits below until the hot water tank asks for it at which point it flows up but this is independent of the motorised valves below?
    It does sound like an intermittent fault with the diverter may be to blame (although having a second unit fail in short order is a bit odd). Worth doing a bit of troubleshooting as per blackalís post at this stage

  11. #11
    Craftsman Gromdal's Avatar
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    Quote Originally Posted by blackal View Post
    A strange set of symptoms.

    1) Can you identify what the 'tank reset' is? Normally for a wet HW heating system you don't need a thermostat reset (I don't think). You do - on an an electrical element stat though.

    2) Simple thing today - is to swap around the motor-valves "heads" betwen HW and CH duty - there should be enough cable there to do that without any faff. BUT - isolate the electrical supplies to the valves, as you will have the cover off the head.

    Then - see how the system operates with the HW control doing the CH and vice versa.

    That should give a fuller picture.

    (if you do have a multi-meter, and are comfortable in its use - leave the head covers off and when you re-energise and signals are fed from the controller to the valve heads - you can check that the signal is getting through.)

    That's as much as I would guess at until you clarify those points.
    Thanks for this - I shall enlist my dad to pop round this evening after work as he has a multimeter and we can check.

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    Master blackal's Avatar
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    Quote Originally Posted by Gromdal View Post
    Thanks for this - I shall enlist my dad to pop round this evening after work as he has a multimeter and we can check.
    Just for clarity - you don't have any cable cores to disconnect, just swap the heads around being careful that you do it with both CH and HW valves in closed position.

  13. #13
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    At my work we seem to have various gremlins with both gloworm boilers, throughout all of our services the only boilers we have issues with are the gloworms for some reason, the company who install them come and fiddle with them and then they work for a short period of time before going wrong again.

    Sent from my A063 using Tapatalk

  14. #14
    Quote Originally Posted by Gromdal View Post
    It was a full replacement, the chap mentioned that they only seem to have a finite lifespan. I'd only been in the house for 3 weeks when they came out and swapped it and it was only 7 years old. I'd be inclined to agree normally but I can't get my head round why it works all the time except when the tank is stone cold, which is why a thermostat fault was also mooted but given that it came on fine this morning in the timer period and was the exact same temperature in the tank as it was last night I'm not so sure! I wondered if there was an issue with the silver box on the left of the picture as this is where the hot water sits below until the hot water tank asks for it at which point it flows up but this is independent of the motorised valves below?
    Do you mean the silver box circled? If so, this is a diverter valve, most likely for your hot water cylinder but canít say for sure without seeing where the pipe from it goes to.

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    Grand Master hogthrob's Avatar
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    Quote Originally Posted by Gromdal View Post
    ...UNLESS the tank has drained itself of hot water, which means that after a bath and a heavy washing up session have exhausted the tank, trying to manually advance the hot water or set to always on results in nothing happening at the boiler, or the diverter valve if the heating is already on...

    If there is still hot water in the tank, does anything happen when you manually advance the hot water or set to always on?

  16. #16
    Craftsman Gromdal's Avatar
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    Quote Originally Posted by hogthrob View Post
    If there is still hot water in the tank, does anything happen when you manually advance the hot water or set to always on?
    Yes, the boiler will kick in if there is still hot water in the tank on when requesting an advance, or setting to always on.

  17. #17
    Master blackal's Avatar
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    Quote Originally Posted by Gromdal View Post
    Yes, the boiler will kick in if there is still hot water in the tank on when requesting an advance, or setting too always on.
    Could be an electrical connection that only makes - when there is heat in it.

    Does happen - and if it is a low-volt signal, wonít arc the same as 230v

  18. #18
    Craftsman Gromdal's Avatar
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    Quote Originally Posted by Craizeehair View Post
    Do you mean the silver box circled? If so, this is a diverter valve, most likely for your hot water cylinder but can’t say for sure without seeing where the pipe from it goes to.
    Yes, that was failing to engage at all when the tank was cold and I asked for an advance/always on HW but I could feel the hot water in the CH system below it (too hot to touch). The part replaced was the left motorised valve at the bottom. When I reset the thermostat on the tank, it would actuate the diverter for the duration of the reset and then lock it off again, so I'd get a spurt of 70 degree water injected into the tank coil and then nothing.
    Last edited by Gromdal; 5th December 2022 at 18:34.

  19. #19
    Quote Originally Posted by Gromdal View Post
    Yes, that was failing to engage at all when the tank was cold and I asked for an advance/always on HW but I could feel the hot water in the CH system below it (too hot to touch). The part replaced was the left motorised valve at the bottom. When I reset the thermostat on the tank, it would actuate the diverter for the duration of the reset and then lock it off again, so I'd get a spurt of 70 degree water injected into the tank coil and then nothing.
    Difficult to say for sure but unlikely to be the cylinder thermostat if itís working sometimes, if itís intermittent I would say itís more likely to be the silver diverter valve to the hot water tank, sometimes the bodyís can get sticky and stop the heads from opening fully and making the switch to power the pump and boiler and sometimes the motors arenít up to the job but they usually fail completely rather than intermittently.

    As you have homecare cover, I think thatís where Iíd be asking them to start, change that silver diverter valve complete, head and body and see how that goes.

    Very difficult to say for sure without having a play with it though

  20. #20
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    You say the tank "had drained itself".
    Surely it should be filling itself back up as you're using it, admittedly not at the same rate as it's emptied but nevertheless emptying it totally would take some doing. Well ours would.
    Are you sure the tank is being filled back up at a reasonable rate, nothing blocking the flow and causing a cut out somewhere due to trying to heat an empty tank?
    Next morning it's full so works fine again.

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