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Dilema with Underfloor Heating and Radiators

Postby Gazzataf » Sun Oct 18, 2015 6:53 pm


Hopefully some kind person here can help with my UFH/Radiator dilema

I have a dual system of which part underfloor heating and traditional radiators. The problem I have is that when the underfloor heating is on the radiators are coming on as well.

The set-up we have is as follows:

* The system is made up of a Baxi Solo 2 60 RS boiler, with Grundfos 3 speed pump (set at speed 2)
* Horstmann Centaurplus C27 series 2 programmer for the boilers CH/HW with a
* Switch-master 3 way valve for CH & HW
* Hot water tank with its own tank thermostat.
* Siemens RDH10 Room stat in the hall for the radiator side of the system.

The UFH details:

The underfloor system which is retro fitted to the above Boiler & CH system, and serves just a kitchen extension on just 1 zone from the UFH manifold with mixer set at 45/50 degrees with grundfoss pump, (No electrical valve actuators heads).
The Flow & return feeds for UFH are taken from the the boilers flow & returns to the UFH manifold and pump system. In line on the flow side there is a 2 way Siemens DVA2/5 valve.
There is also a small ballofix (i think that's what he called it) check valve between the Flow & Return just above the Siemens 2 way valve?.
The UFH is controlled by a programmable heatmiser thermostat in the kitchen.

I know in order to run the underfloor system efficiently, I should have it programmed to come on constantly and operate efficiently by the set of the temp/time of the thermostat, but this is proving difficult as the radiators keep coming on as well despite the radiator thermostat being off?.
This is also an annoying nightly occurrence as well, as when the temp drops and UHF kicks in the rads warm up unless we switch it all completely off.
I am therefore not getting the best benefit of the underfloor heating? As it is diverting the water to both systems making it less efficient .

I would be grateful if someone can offer advice as to what might be wrong ? I would like to try some troubleshooting before I try and find a specialist underfloor engineer?.

Thanks in advance
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Simply Build It

Postby thedoctor » Thu Oct 22, 2015 8:54 am


Issues such as these can be pretty tricky to diagnose - from your explanation it does sound as if there is possibly a faulty valve in the system not doing what it’s suppose to i.e. it’s opening when it shouldn’t, supplying both systems when it should only be supplying the one.

In light of this, I think you are probably going to have to bite the bullet and get someone in to thoroughly test the system to find out what’s at fault.

Hope this helps

Kind Regards
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Joined: Sat Apr 08, 2006 12:15 pm

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