Central heating problem. Please help

I have a Ideal Icos boiler in my home which is used for hot water & the
central heating which incidentally is a unfloor heating system. Since the past couple of days the boiler does not fire up for the central heating. The UFH system looks to work perfectly fine & there is a proper water circulation and all usual trouble shooting techniques with UFH does not
reveal any issue. Assuming the UFH system is working fine, I am struggling to find out why the boiler does not fire when the Central heating demands it.
Hot water is available whenever required and boiler only fires up for it.
Could someone please help?
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pushps wrote:

Need to tell us whether the ufh runs off boiler or electric. Need to tell us what youve checked already. Have you had a multimeter on the programmer & stat outputs to see theyre really working?
NT
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pushps wrote:

Sounds similar to my system.
Now te hpath te electrons take is generally this.
Main heating isolation switch. That has to be on for anything to work. You have HW so that's not it.
Master timer/programmer..and thermostat...you say that you have water flow in the UFH..so one can assume that the auxiliary pump for UFH is working? If that is so then you can eliminate the thermnostat and teh timer..they control that pump.
NOW it gets trickier. In my setup - and yours probably - the stat and programmer run a motorised valve, and the output of that controls the aux pump as well as opening up part of the heating primary circuit. HOWEVER with a secondary pump, there is one issue..in order for e.g domestic HW to NOT fire up the aux pump, you cannot have both pumps wired in parallel, In my setup a relay is used to provide an extra contact for the boiler and its pump, fed from the same circuit as controls the aux pump. If that relay fails the boiler will not fire up.
You can test all this by getting the boiler to fire using e.g. the domestic HW to come on as well..if that results in hot water under the floor then the UFH circuit is simply not calling the boiler, but the boiler itself is working. That's the relay in all probability. It will be a simple plug in thing somewhere in the wiring box..
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Thanks for the input guys. Not being a technical person, it kind of does not make much sense to me. The UFH is triggered by the gas boiler. The system is a combi boiler and the HW is not exactly run on demand. It stores itself in the unvented tank and is used from there. The boiler triggers when the timer triggers demand for HW.
I could feel the flow in the UFH system by touching the manifold pipes. Although the pipes feel cold to touch and only warm when the HW has triggered the boiler but never hot. Someone asked me to check the actuators and they seem to work as the caps pop up when the UFH timer is triggered.
The return pipe on the UFH is always cold.
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pushps wrote:

Then strictly it is not a combi..

Have you an auxiliary pump on the UFH?
If so, is it working?

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