Zoning a combi

Discussion in 'Plumbers' Talk' started by Rmprop, Jun 12, 2016.

  1. Rmprop

    Rmprop Member

    I'm renovating my house which has a combi controlled central heating and hot water system already in place. I've changed all the rads to cast iron without trv's and would like to change the system to a 2 zone - upsairs and down stairs with a thermostat to control each zone. It already has a basic wireless stat and the timer is on the boiler.

    What I was hoping to do is keep the timer as is, so the current stat opperates all the system, but have the upstairs on a seperate stat so it can turn off that part of the heating when it gets to temperature. Its an old house and the ground floor is really cold compared to the rest of the house, so when the heating is on and the ground floor is up to temp, the rest of the house gets really hot as the rads are still kicking out heat up there.

    I've looked on Google, but all I seem to find is drawings for heating systems with hot water tanks, which we don't have. My question is what is the best aproach, is it a simple case of adding a 2 port zoning valve to the upstairs feed loop? Do zoning valves have to have their own timer or can it just be conected directly to a room stat?

    Thanks...
     
  2. Dave does Gas

    Dave does Gas Screwfix Select

    Two port like you said which is opened and closed by a thermostat is the simplest but you can have different times up and downstairs if you want. This system is widley used in HMO's nowadays.
     
    KIAB likes this.
  3. Rmprop

    Rmprop Member

    Thanks. How is the zone valve connected to the stat, is there some sort of controller that its wired to which recieves the signal from the stat (if I use a wireless one)?
     
  4. nigel willson

    nigel willson Screwfix Select

    therostat/timer controls the motor in the zone valve, the switch in the zone valve fires the boiler. when the valve is fully open.
     
  5. Rmprop

    Rmprop Member

    I don't want it to control the boiler as the thermostat it currently has will do that. I just want the zone valve to shut upstairs off when it gets to temp, whilest downstairs(controlled by the stat it has now) carrys on heating until it gets up to temp too.

    If the timer/stat controls the valve, can I go wireless, I assume it would need some sort of wireless reciever on it for a wireless stat to operate it?
     
  6. sam spade

    sam spade Active Member

    You need to check the pipe runs to make sure the upstairs rads can be shut off without affecting downstairs rads.
     
  7. Rm, there's a few issues involved here.

    The first is as Sam says and that's to check that the upstairs if essentially supplied by a single 22mm pipe so that the upstairs 'zone' can be isolated as required.

    The proper way to then control it is to install a room/wall thermostat (or Prog Stat) to control the upstairs and this will first trigger the zone valve as required which will then control the boiler independently of the downstairs. That's the usual way.

    However, you aren't bothered about this kind of separate control - you are happy that the upstairs will only ever need heat when the boiler is already on supplying the downstairs? So that does make things slightly easier.

    However, there is another issue - ALL the leccy wiring and components for your system should be isolated by a single DP switch. So, really, even if you want to keep it simple, you should still run the power for this valve and thermostat from the same switch/wiring centre as does the existing system.

    Apart from that, it's a relatively simple case of fitting a zone valve and having it powered by your room/wall 'stat.
     
  8. Rmprop

    Rmprop Member

    I have re done all the pipe work in 22mm as it was all done in 15mm and not clipped anywhere, and made all kinds of clicking and clunking noises while it warmed up. I've done it as 2 loops - one down stairs and one up.

    When you say a single pipe, I take it you mean 1 feed pipe for that loop? Does the return need a valve too?
     
  9. Jitender

    Jitender Screwfix Select

    I was thinking of zoning my system to.

    You would only need a two port on the flow.

    I am looking at getting the nest wireless stat, but it would require 2 x thermostats + 2 x heat links.
     
  10. Glad its Friday

    Glad its Friday Active Member

    Whatever you decide to do, if using 2 port valves make sure that you fit a by-pass so that when the valve(s) close the boiler can pump the hot water away somewhere.
     
  11. Rm, yes, just a valve on the flow.

    I don't think I'd worry in your case about fitting a by-pass valve as mentioned above, as your upstairs will only be on if the downstairs is too - and the downstairs will either already have a by-pass (a bathroom rad with no TRV, for example?) or the boiler will have one built in. But, fair point - worth confirming.

    Please do consider the point about having it leccy-powered from the same single boiler supply point - this is a regulation as well as simply being sensible. Plumbers/sparkies expect the whole system to be dead when they isolate that single point.
     
  12. Glad its Friday

    Glad its Friday Active Member

    DA - read the original post. ".....and would like to change the system to a 2 zone - upstairs and down stairs with a thermostat to control each zone". Which means that there could be a situation when upstairs could be on independently.
    With 2 port valves, always fit a by-pass, save yourself lots of trouble later on.
     
  13. sam spade

    sam spade Active Member

    1, Have the radiators been balanced?

    2. Why no TRVs on the radiators upstairs? If you are installing a new system (which in effect you are) TRVs are required to comply with Building Regulations.
     
  14. Yes, but he also made the point that, in his case, the upstairs wouldn't be controlling the boiler independently - just able to turn on the rads as required when the system is already on.

    But fair point.
     
  15. Do'h!

    Yup - obvious Q!

    (Tho' not obvious enough... :oops:)
     

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