Underfloor Heating - Pump switch in manifold not working? Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[Thornhill]

I recently had a Speedfit underfloor heating pack installed.
It links in with my existing boiler/rad system with a separate circuit. It has a room thermostat & controller and its own pump which appears to be controlled by a thermostatic switch in the manifold.
The thermostat & controller appear to be working fine and the boiler fires & valve opens, but the pump on the manifold does not start.
It appears to be linked to what I can only assume is a thermostat in the manifold and when I by-pas this swithch the pump works and the floor heats up.
Clearly the manifold switch/thermostat is there for a reason, but I'm nor really sure just how it's all supposed to link togther.
Do you think that the unit is faulty or does the water need to heat up before the pump fires?
I don't really want to run with my temporary fix, so any information or advise would be great....Thanks.

P.S. Not really on speaking terms with the Plumber/Builder, so reluctant to go via this route!

[The Heating Doctor]

What temperature is the thermostat on the manifold set to? Is the manifold built in or is there plenty of air circulating around it?

[Thornhill]

I have the temperature on the manifold thermostat on Max, but have tried changing this.
The Manifold is enclosed, but have removed all of the enclosure for access, but this does not appear to make a difference.

I'm not clear on what this thermostat should do.

[Thornhill]

The Manifold Thermostat is on Max, although I have tried Min setting.
It is in an enclosed space, but I have removed the panels for access so is currently open, but does not seem to make a difference.

I'm really not sure what this thermostat is supposed to do, should it trigger the pump when the temperature drops, or when it rises?

[The Heating Doctor]

The thermostat is a over heat thermostat which will shut your pump down when activated. The reason I asked if it is built in i.e. coverd is that heat rising from the manifolds can build up and trigger the thermostat if not allowed to disapate. Having spoke to Speedfit about a similar problem, just last week, there soloution was to set the thermostat at 90 deg C. This I would have thought negated the point of having a overheat stat however when done this solved the problem. The thermostats they provide are a mechanical thermostat which are known for there inaccuracy (most mechanical stats not just Speedfit). If you have a particularly sensative unit it could be switching well below the set point figure on the dial. As your system is a recent installation you have a two year warranty therefor I would contact your installer to rectify the fault via Speedfit.

[Thornhill]

Thanks for your thoughts Doctor, I will reset the thermostat and try again.

However, I've re-read the documentation that came with the unit and am slightly confused as to how it can ever work!
The documentation suggests that the internal thermostat switches the pump off at about 30 degrees and switches it on at 45 degrees - can't remember the exact numbers.
What I don't understand is when it's switched on from cold, how will the water at the manifold ever get to 45 degrees without the pump running?
Do we need to assume that sufficient heat will be conducted around the pipes/water to heat the manifold?
If so, maybe I need to leave it switched on for longer to allow it to heat up sufficiently?
Am I being stupid or am I missing something?

[The Heating Doctor]

The water deliverd to the manifold will be around 80 deg C from the boiler and gets there by means of the boiler pump, so it should not take long for the manifold to reach 30 deg C. The underfloor water should run around 40-45 deg C. Hope this helps

[Thornhill]

Thanks again Doctor, that does seem to confirm my understanding, but does concern me a little. Let me try to describe the set-up ....

The UFH has been added to an existing system. Original set-up is as follows. Boiler leads to pump, which leads to T-junction. One side has valve and leads to Rads; other side has separate valve and leads to cylinder. All controlled through a control box and thermostats on wall & cylinder.

The UFH is spurred off the system BETWEEN the boiler & main pump. It has a valve which is controlled by a separate thermostat & control unit. The control unit will activate the valve & fire the boiler but will not trigger the main pump. The manifold pump is independent of everything as discussed.

My concern is that if the UFH is switched on, but the Rads & Water are not on for any reason, the boiler will/does fire, but the main pump is not operative. I'm not sure that the pump would be much help anyway, as it is after the UFH spur on the circuit and the other valves will be closed.

Q. How does the hot water get from the boiler to the manifold to trigger the manifold pump?
I can't see this set-up working unless the Rads and/or Water happen to be on!
Any thoughts?

[The Heating Doctor]

Your htg engineer has got it wrong based on what you have explained.

When the Underfloor heating has a demand both the manifold & main pump MUST run. The underfloor should have a Speedfit wiring centre part number JGUFH4ZM from which the wiring for the Actuators on top of the manifold, the underfloor pump & boiler are wired from. In this wiring centre there are a set of terminals for a motorised valve which should go to the "valve" you say is activated when the underfloor is needed. Now hopefully the heating engineer has used a Honeywell or Drayton or another manufacturer who fits an end of travel switch in the valve motor head if they have the engineer can use that switch to start the pump. I hope this is making sense. What I'm saying is the thermostat calls for heat, this opens the valve, when the valve is fully open it closes the end of travel switch which is built in to the valve, this starts the main pump & the wiring centre starts the boiler, maniflod temp rises, u/f pump starts, problem solved. To get this to work the engineer needs to run a cable from the valves switch to a relay, take all the other main pump feeds i.e. hot water on and radiators on, to the same relay and in the event of one or all asking for heat the pump will start. Phew!

[Thornhill]

Thanks again Doc.

I think that what you are suggesting is correct, but requires some changes to the pipework also...
The current configuration has the UFH spur between the Boiler and the main pump. If the pump is started and the Rad & Cylinder valves are both closed then there's a problem.
I think that the UFH spur should be after the pump, to ensure that therte is a flow to th valve (which will be open) and the manifold.

Does that sound right?

[The Heating Doctor]

That is correct, the main heating pump must be able to feed the underfloor manifold even if the rads & cylinder are shut off. This is because unlike the rads & cylinder the underfloor works 24hrs/7days.