wiring diagram please

Discussion in 'Electricians' Talk' started by deeps, Nov 6, 2014.

  1. deeps

    deeps Member

    Hi just purchased a new property.
    Boiler fitted is a ideal c80ff, it has a external timer dual channel and room stat.
    I have had the boiler serviced by british gas, boiler working OK BUT the electrics are all wrong.
    I have purchased a single channel timer and going to disconnect the room stat as all rads have thermostatic valves.
    can anyone please provide a wiring diagram that I could follow to connect the boiler to a Drayton LP711
    many thanks
     
  2. spinlondon

    spinlondon Screwfix Select

    Are you sure that the room stat is connected?
    If all the rads have thermostatic valves, there should not be a room stat.
     
  3. deeps

    deeps Member

    yes its connected via jb which is in a pitiful state wires twisted together and taped. What i want to do is disconnect everything and start again.
     
  4. unphased

    unphased Screwfix Select

    Don't disconnect the roomstat! It is a common misconception that you don't need a roomstat with TRVs. You do! If you take the roomstat away you will use much more gas as your boiler will be cycling on the boiler stat. Plumbers are the worst culprits telling people they don't need a roomstat. Always always always fit one. :)
     
    Jitender and FatHands like this.
  5. unphased

    unphased Screwfix Select

  6. spinlondon

    spinlondon Screwfix Select

    It's not a misconception.
     
  7. stateit

    stateit Screwfix Select

    Building Regs now require a roomstat and TRVs

    And the room a stat is in not to have a TRV on the rad.
     
    Jitender likes this.
  8. unphased

    unphased Screwfix Select

    Yes thats correct. Lock shield valve on rad where roomstat is located.
     
  9. MGW

    MGW Screwfix Select

    It would seem there are a few different ways to control. There are some boilers with anti-cycling software and by-pass valves which rely on the TRV for the system to work.

    Others don't have the software and/or have not got a by-pass valve and require one radiator to have no TRV.

    Others have a thermostat outside which stops it firing up in the summer when the day is likely to be warm.

    There is a problem with the simple TRV in that it is only set to one temperature. In my house the thermostat can have 8 temperatures set 4 Monday - Friday and 2 Sat and 2 Sun and the system is not turned off by any clock it just changes the temperature setting which means no frost stat is required.

    The TRV heads can be changed for WiFi versions which then allows each room to be controlled with both time and temperature from a master controller so for example bedrooms only have heating from 10 pm to 8 am and living rooms 7 am to 11 pm even connected to the intruder alarm so once set heating only stops freezing.

    The NEST system allows control from the phone.

    Where the problem arises is where one tries to mix and match. Each works well but try mixing and the TRV will open but there is no hot water being circulated.

    The basic idea is the lock shield valve ensures on start up hot water arrives at every radiator and the return water will be quite cool. As the rooms warm up the TRV will close as a result more water will be forced through the remaining radiators as a result the return water starts to get warmer and warmer as each TRV closes. When so many have closed the by-pass valve starts to open. As the return water warms up so the flame hight on the boiler reduces. Until it reaches a point where it can't go any lower. At this point the boiler switches off for a set time. After the time has elapsed the boiler restarts if the TRV's are still closed hot water will return quickly and the time before it re-tries is increased. If however cold water returns the re-try time is decreased. This way there is no need for any electric thermostat. However during the summer the house could be warmed up in the morning and then as the day progresses it gets too hot. Placing a thermostat where it gets the morning sun stops this from happening.

    For the above to work ALL radiators must have TRV's and the boiler must have anti-cycle software and there must be a by-pass valve. If some plumber has left one radiator without a TRV then the anti-cycle software will not work. If the by-pass valve is missing then it will damage the pump. If the boiler does not have anti-cycle software the pump will never switch off.

    Although is sounds good there are problems. Most people don't want TRV fitted to towel rails. Radiators like the Myson allow too much hot water back to the boiler which turns the flame hight down. If the lock shield values are incorrectly set it can end up heating one room at a time and can take an age to heat whole house.

    The lock shield valve is a real problem with condensing boilers either much stops a radiator working or they are left wide open and the boiler only runs at reduced output.

    I can see why people want to use the old system. An electric thermostat with varying temperatures like mine seems to make sense. But only with an open plan house. My house was designed to be heated by one central gas fire. With no door living room to dinning room or living room to stairs a single thermostat works. I have TRV's upstairs to stop bedrooms over heating but non down stairs.

    But take a house with doors between the rooms and where ever you place a single thermostat some room will end up cold. Even wind direction can cause havoc which is a problem with my mothers house. Wind from North not a problem but get it from South and the single thermostat in hall closes down the boiler even though the living room is cold.

    What I am saying there is no one size fits all and trying to heat every house with the same system just does not work.
     
  10. There are a lot of wrong assumptions above.

    Just one is about the balancing of rads. The lockshield has to be set exactly to provide the required temperature drop across the rad.

    Smart pumps provide a constant pressure head and prevent balance changing as some TRVs are closed. But they are incompatible with auto bypass valves.

    Tony
     
  11. nigel willson

    nigel willson Screwfix Select

    Boiler interlock!!!! is the term ur all looking for
     
  12. sinewave

    sinewave Screwfix Select

    A Room Stat should always be fitted, and as said, the Rad in that room should have no TRV.

    We have a 3 story House and each floor has it's own pumped loop fed from a Low Loss Header.

    Each floor is controlled by it's own Digi Stat giving total independence for each floor.
     

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