I bought my first house in December and one thing I've noticed over the winter is higher than expected gas usage which I'd like to try and get down if at all possible. The house is a three bedroom (two plus box room really) semi-detached UK house built in the 30s if thats relevant. The previous owner had recently installed a new Ideal Icos HE24 combination boiler but with a standard thermostat and timer.

I'd like to replace the thermostat and timer with two programmable thermostats for upstairs and downstairs and use valves to control heating flow to the two zones. I've seen drawings on the internet showing this using a standalone boiler with separate pumps wtih each zone but am not sure if zones are achievable using combination boilers or whether I'd be placing stress on the boilers internal pump?

My thoughts so far involve one valve for the upstairs flow and one for downstairs flow, from what I've seen I don't need return valves as well?

Working with heating systems isnt something I've done before so I guess I may have some things wrong here but would be interested to hear peoples thoughts.

5 Answers 5


As long as the boiler is capable of providing enough hot water through the system to heat the whole house if necessary you shouldn't have a problem.

What you are proposing is a "coarser" version of thermostatic valves on each radiator and that is perfectly safe for a combination boiler.

I don't think you need return valves.

Make sure that you leave one radiator "open" (usually the bathroom one) so that there is some flow around the circuit.

By the way the fact that it's a combination boiler is a red herring. The "combi" bit refers to the hot water heater, the central heating aspect is pretty much the same as a "standard" boiler with integral pump.


If you want to control the times each room is heated independently you can get combined timer and thermostatic radiator valves - My Greener Home has some for example.

  • It is likcly that a "open" radiator is not needed, just the docs for the boiler. Most boiler that are sold these days will dedect when there is no where for the water to go and turn themselfs off.
    – Walker
    Commented Jul 28, 2010 at 20:38
  • I was thinking of using thermostatic valves on most radiators as well, this was mainly so that both floors of the house were not being unnecessarily heated when only one was needed. However now that I think about it more, the better/cheaper option might just be radiator valves and the gain might be negligible by using zones.
    – Duncan
    Commented Aug 1, 2010 at 14:47
  • @Duncan - the only benefit "zones" gives you is separate control over the times when each zone is on/off. It's been a while since I checked but I'm fairly sure you can get combined thermostats & timers for individual radiators.
    – ChrisF
    Commented Aug 7, 2010 at 18:11
  • Thanks Chris, those units from My Greener Home look very interesting and I'll probably end up getting some of those.
    – Duncan
    Commented Aug 10, 2010 at 21:56

Just putting thermostatic valves on each radiator is the standard solution these days.

However having zones will you set each zone to come on at a different time as well as giving them their own thermostat. You can do anything with a combination boiler that you can do with a system boiler of the same rating.

You may not even need to add a 2nd pump if you design the system carefully.

Remember last winter was very cold by UK standards, so it is not a good indication of ongoing gas usage.


Worth noting that unless your two zones are well insulated from each other, you will lose heat across the gradient of heated to unheated rooms, so you'll effectively be heating the whole house using 'half' of the heating. It will be interesting to see how much efficiency you actually gain given this complication.

  • Yes, but this is no different to having radiators turned off in some rooms and on in others.
    – Chenmunka
    Commented Sep 2, 2021 at 8:06

I am not an expert on the subject, but when we were buying our house, inspector noted that heating system has three separate pumps for the three zones. He said, that it was "nice", and "more reliable then a single pump". From this I draw a conclusion that it is possible to run multiple zones off of a single pump, but you probably want to avoid doing that.


More than one zone is the ideal solution and will be far more efficient than using radiator valves however not so easy to accomplish in an existing system depending on access to your plumbing. Zoning is achieved by using a solenoid valve for each zone - 2 in your case after the pump. You only use one pump. The Thermostats - 2 in your case control the solenoid valve. So when your downstairs thermostat calls for heat it opens the Solenoid valve, the pump starts and your boiler goes into action. Same for upstairs. They are completely independent. I have put an extra zone in my conservatory with its own Thermostat so when its cold outside I can keep the conservatory at a toasty 21deg with one radiator without affecting the rest of the house.

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