Posting a message to the forum will remove the above advertisement
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. Checkout our Plumbers Insurance area - heavily discounted Public Liability Insurance and Van Insurance specifically designed for plumbers.

Discuss DHW Temperature Drastically Fluctiating when CH is on. in the Plumbing Forum area at

  1. perky416

    perky416 New Member

    Evening all.

    Last month i had a new Worcester Bosch Greenstar Compact 32CDI combi installed. I have come to notice that when the CH is on there are drastic fluctuations in the temperature of the hot water when the tap is on. The water temperature is currently set to 46 degrees on the boiler. I tested the fluctuations with the thermocouple on my fluke multimeter. When turning the tap on the cold water naturally comes out the pipe, then the temp goes up to between around 36 and 46 degrees, then back down to around 17 degrees, then up to around 36 degrees, then back down to around 25 degrees, then back up to around 36 degrees before it very slowly climbs into the 40s over the next couple of minutes. The temperature is fine when the CH is off, After the cold has come of the tap I am getting a very constant temperature in the mid 40s.
    Surley it cant be normal for the temperature to fluctuate so much? Please could somebody help shed some light on the issue? Should I get on the phone to worcester bosch?

    Many thanks.
  2. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    set the water temperature to 55 and see what happens then. cheers kop
    • Useful Useful x 1
  3. scott_d

    scott_d Plumber GSR

    Could it be a mixer tap passing?
    What did you have before the WB?
  4. perky416

    perky416 New Member

    It was originally set to 55 and the same thing was happening. I turned it down when investigating the problem as it was a bit hot having my hand under there before I got the thermocouple under it.

    It is a mixer tap in the kitchen, i originally thought this was the problem however when flushing the newly fitted pipes in the bathroom a couple of days ago i noticed the fluctuations, no tap this time just an open pipe, thats what made me realise there is a problem. It was a WB conventional boiler fitted before but i never used it, been in this house a little over a month and the first thing i did was rip out the old system.

    Thanks guys.
  5. Riley

    Riley Plumber GSR Top Contributor!!

    Who fitted it?
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Is this with the tap fully open if so do your tests with the tap only half open
  7. perky416

    perky416 New Member

    It was a gas safe engineer.

    It was with the tap fully open. I have just tried it half way and the temperature went up to around 48 degrees before dropping all the way to 8 degrees where it sat for a few minutes. I had to open the tap fully to get it to go up again where it then jumped between 32 and 25 degrees a few times before settling at 32.
  8. Riley

    Riley Plumber GSR Top Contributor!!

    I’d get the fitter back. I assume it’s under warranty?
  9. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Contact worcester it will be under warranty . cheers kop
    • Like Like x 1
Similar Threads - Temperature Drastically Fluctiating Forum Date
Advice really appreciated on hot water temperature Central Heating Forum Yesterday at 7:47 PM
Thermowatt 143 - what is its temperature range? Central Heating Forum Sunday at 9:36 AM