Thermostats and pumps - What's the trigger?

Bradds

Hi Folks, first post!
                I have an underfloor heating system with 9 zones that was installed in 2003 with 4 wire, 230V Danfoss actuators and hard wired Danfoss TP5 thermostats which trigger the pump circulating through the zones. The heat is supplied from a biomass boiler in the garage through a heat exchanger into the manifold. The boiler comes on at set times during the day and delivers heat to the manifold, which then distributes based on what the zones are calling for.  Over the years I've replaced 3 actuators when the rooms were failing to heat, and had little other issues.
      I've now discovered that a number of the thermostats, whilst calling for heat, are not activating the pump. I can resolve this by increasing the required heat on one of the other thrermostats to 'click' and call for heat and the pump kicks in shortly afterwards. Therefore it's not the pump.
       Crucially though, when the pump is running, the heat is being delivered to the zones that are requesting it, so I suspect the actuators are OK too.
My question is then: Is it thermostat that triggers the pump, or is it the actuators? The thermostats are 'clicking' when calling for heat but I'm not sure if that signal is getting to the pump. Happy to replace the thermostats, but I'd just like to be reassured that they can fail in a way that they stop physically requesting heat.
Thanks
Graham

matelodave

If you've got 4 wire actuators then the the actuators should start the pump and boiler when they open. The second pair of wires are connected to a normally open microswitch which should  close to operate a relay to start the boiler and pump. Have you got a manifold controller or are the stats wired directly to the actuators? Where is the control pair terminated?

My system has 2-wire actuators which are connected to a manifold controller. The controller activates the actuators as well as the heatpump (both compressor and circulating pump) whenever a thermostat calls for heat. All the stats are programmable so anyone of the eight zones can activate the heating whenever they call for heat.

I guess some of your actuators haven't been wired correctly and don't activate the pump/boiler. However that said, does the u/f heating have it's own circulating pump in which case you might find that the actuators just fire up the manifold pump and don't control the boiler and main circulator

tacpot12

i thought it was normally a control unit (e.g. Danfoss FH-WC) that all the thermostats and actuators are wired into that controlled the pump, so that when any thermostat was calling for heat, the pump would be turned on only when enough time had elapsed for the actuator to move (although you can get 4 wire actuators that signal when the are open). 

I think the most likely explanation is that some wiring between some of the TP5s has become disconnected. A simple thing to troubleshoot if you are confident you can safely isolate the heating system. 

Has there been any building work or water leaks in the house that might have caused a problem? 

Talldave

I'm not familiar with Danfoss stuff, but can you swap over a "faulty" and "non-faulty" thermostat  between rooms and see if the fault moves rooms or stays? If the former, it must be the thermostat,  if the latter,  it's either the wiring to the "faulty" room or more likely the wiring centre. My guess would be that a call for heat to the wiring centre/hub/whatever Danfoss call it, will trigger the actuator and call for heat from the boiler (ie: trigger pump), it's unlikely there are two signals. Therefore my guess is the fault might lie in the wiring centre/hub thingy.

Final thought - are the actuators like traditional motorised valves where they close a contact on fully opening and it's that that loops back to the boiler to call for heat?

matelodave

Most manifold actuators have thermal wax motors that heat up slowly (3-4 minutes) to open the manifold valves. As I said above 2 wire units just open and close when power is applied but those with 4 wires have a microswitch which operates when the valve is opened and it will then enable other functions in the system.

It depends how your system has been configured whether all the stats operate the boiler or just a couple of them - you need to check out how it all been wired.

Bradds

That's great everyone, and really helpful. I did have a house leak last Christmas that flooded the upstairs and downstairs hall, but Didn't get near any of the wiring (I think). Given that 3 of the other actuators have failed over the years (wax type), it seems likely that others have now failed in a different way and they now don't send signals to the main pump on the manifold.  The 4 wires from the actuators are all terminated in a 'big box full of wires' above the manifold. The boiler is essentially completely independent with its own pump on a seperate circuit. It's a biomass boiler, so I choose to run it on a timer.
      I have a couple of spare actuators so I'll replace one I know definitely isn't working and see how it goes. Thanks for the advice!