Cold Water turning off Boiler Flame

Discussion in 'Plumbers' Talk' started by Sonofabrit, Oct 8, 2018.

  1. Sonofabrit

    Sonofabrit New Member

    Hi all,

    I have an odd issue with our deck mounted bath/shower mixer. Similar to this
    https://www.screwfix.com/p/swirl-contract-deck-mounted-metal-head-bath-shower-mixer-tap/61344

    When having a shower turning on the hot water, boiler fires up as normal. If we turn on the cold water to regulate the water temperature and to get a bit more pressure it instantly knocks out the boiler flame.

    No other taps do this, Kitchen or the Bathroom Sink. Can have hot and cold taps fully open on either of those and the boiler will remain on.

    If running a bath with both taps fully on as well, the boiler will stay on. Only when using the shower and opening the cold water tap knocks out the flame..

    We have tried adjusting the water temp on the boiler itself to be lower for the hot water to get some more flow, but still same issue.

    Can anyone help/point in the right direction to tackling this issue? (driving the mrs mad) Is it case of putting a NRV on the hot or cold water pipes on the bath mixer?

    Thanks in advance
    John
     
  2. KIAB

    KIAB Well-Known Member

    What make & model is the boiler, & it's age.
     
  3. retiredsparks

    retiredsparks Well-Known Member

    I would look at the shower/bath selector mechanism.
    Rs
     
  4. terrymac

    terrymac Well-Known Member

    What happens if you turn cold on first ,then divert to shower head ,then put hot on full, and then slowly close down the cold till you get the temperature that you want ? Does the boiler then close down ?
     
  5. The Teach

    The Teach Well-Known Member

    Assuming its a combination boiler,the internal hot water proving switch could be sensing insufficient flow and shutting down when cold water is selected on the shower mixer.

    Could be many other faults aswell :( Info helps :)
     
    kitfit1, Crowsfoot and DIY womble like this.
  6. Sonofabrit

    Sonofabrit New Member

    Thanks for all of the replies!

    "What make & model is the boiler, & it's age."
    - It is a Main Combi 24 HE, reckon it is 9 years old.

    "What happens if you turn cold on first ,then divert to shower head ,then put hot on full, and then slowly close down the cold till you get the temperature that you want ? Does the boiler then close down ?"
    - WIth cold water running first, and then turning on Hot the boiler doesnt fire

    "I would look at the shower/bath selector mechanism."
    -I have thought this as well in the past, have replaced the flexible shower hose it rule out any kinks, as well as the shower head in the past, no difference. The rubber washers all look to be in good shape, the only thing that hasnt been changed is the actual deck mounted component.

    "Assuming its a combination boiler,the internal hot water proving switch could be sensing insufficient flow and shutting down when cold water is selected on the shower mixer. Could be many other faults aswell :( Info helps :)"
    -We have had a gas/plumbing engineer around in the past to do yearly checks, one "diagrpham" has been replaced, cant remember what it was called exactly but it was a 3odd inch round diameter rubber gasket looking thing, I vaguely remember him saying it was related to flow (although my memory could be making this up :p ) . Have also had a ?pressure balloon? - forgive the terminology that had to be pumped up with a hand/foot pump tool as the pressure kept dropping about 2 years ago (pressure has remained fine since)
     
  7. Crowsfoot

    Crowsfoot Well-Known Member

    Just a quick question Sono.
    Is the shower head running freely with none of the holes blocked up?
    The Teach is probably on the money.
    Suggestion - open the hot tap on the wash hand basin at the same time you shower and see if the boiler cuts out then.
     
  8. terrymac

    terrymac Well-Known Member

    Has this mixer / shower worked well in the past ,and your problem recently arose, or is it a new mixer ?
     
  9. kitfit1

    kitfit1 Well-Known Member

    If you are suggesting low cold water pressure, and i think you are, then i agree. Had this same issue myself about 5 years ago, finally tracked it down to a leak on STW's stop tap in the street. It was leaking big time, but not showing up at pavement level, so it was never noticed.
     
  10. Sonofabrit

    Sonofabrit New Member

    Thanks again for the replies, sorry for the delay getting back.

    "Is the shower head running freely with none of the holes blocked up?
    Suggestion - open the hot tap on the wash hand basin at the same time you shower and see if the boiler cuts out then."
    Shower head is running freely, it was replaced about 2 months or so ago. If we open the hot tap on the basin after the cold tap from shower cuts out the boiler, it takes up about 50% of the flow of hot water to the shower, but it does kick the boiler back on, but it has to be fully open on the basin, half way doesnt do it.

    "Has this mixer / shower worked well in the past ,and your problem recently arose, or is it a new mixer ?"
    It used to work fine 2 and a bit years ago, gradually got worst over time. The mixer has to be 9+ years old as well.

    I have found if we turn the flow valve on the cold water pipe to the bath/shower to be about a 1/4 way open it allows us to have a shower without knocking out the boiler, but at that flow rate the cold water is basically trickling out.
     
  11. The Teach

    The Teach Well-Known Member

    As long as the combination boiler is producing hot water as it is expected to (that fact is very important especially with the boiler mentioned) ,then the current bath mixer arrangement would need specific installation to provide its safe to supply a shower attachment. A thermostatic bath shower mixer or a thermostatic mixing valve in the flow stream to the mixer will give anti scald protection.

    Very often the mains cold water supply to a shower heated via a modulating combination gas boiler will need the mixer to be restricted to approx 4 liters per minute flow. Thats to prevent mains cold water starvation at the boiler inlet interfering with any hot water proving device & other reasons.

    having the bath flow cold bath flow limited to 4 liters per minute can be bothersome for many users but it gives the modulating combination boiler a chance to maintain an average shower temperature.

    For anti scald reasons the best remedy is to fit a governed thermostatic bath shower mixer or incorporate a thermostatic mixing valve in the shower flow. then it can be classed as a shower.(otherwise its just an an assisted bath shower mixer attachment).

    this bath mixer with shower attachments work well and is anti scald.https://www.idealspec.co.uk/catalog...-100-rim-mounted-bath-shower-mixer_p1090.html
     
  12. Sonofabrit

    Sonofabrit New Member

    Thanks Teach.
    Was thinking of getting a thermostatic mixer previously, just want to make sure before putting down the ££'s.

    Is it possible with the standard mixer that I currently have with the cold water pressure being higher than the hot, that when I use the shower and it has to be forced up the shower hose with the hot water, the pressure is too high for the shower and the cold water is being forced down the hot water pipe, preventing it's flow and knocking off the boiler flame, or is that just crazy thought? Hence the potential thought of a non return valve on the hot water pipe to prevent this (if that's even plausible)
     
  13. The Teach

    The Teach Well-Known Member

    The situation is the cold mains water is most probably starving the combination boiler of sufficient water flow to operate its hot water switching. Have to assume the combination boiler is in excemment well serviced working order,your combination boiler is a modulating gas appliance and has a few red flag faults that can occur during shower operation :( only onsite testing will tell.

    Think about purchasing showering products made in the uk for uk water systems,sf sell some ***** which need professional installation at extra cost
     

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