UFH pump not turning on

Hi all,
I've noticed that my UFH pump is not always turning on as soon as the stat & valve calls for heat. This results in hot water passing through the underfloor pipes but without being pumped, which means it takes forever for the room to heat.

From testing with a multimeter I see that it's not a problem with the pump, it just isn't always getting power sent to it.
I can see that the live to the pump comes via the UFH manifold. Is this part of the intended design? E.g. the manifold is meant to choose when to turn the pump on? Something to do with water temperature?

Sometimes the pump will come on immediately with the stat calling for heat, but most of the time it doesn't - and to be honest it seems to be pretty random.
Extensive googling and checking instructions for this manifold/pump hasn't come up with anything helpful - everything just says to check the pump isn't jammed!

There are usually Pump L-N-E terminals in the manifold control center, if the pump cable isnt connected to these it has been wired incorrectly.
If it has maybe a link is missing but if it has been working ok previously maybe a faulty panel?
Yes something to do with temperature, the room thermostats start the process of operation with set temperatures, on more complex systems an Hi temp thermostat may prevent the system as a whole from working not just the manifold pump.

It's hard to tell from that picture, does the pump cable connect to a device attached to the manifold behind it?
It looks to me.like the type of system that uses a temperature operated switch in the manifold to control the pump, in which case its probably that temperature operated switch misbehaving.

DefyG said:

There are usually Pump L-N-E terminals in the manifold control center, if the pump cable isnt connected to these it has been wired incorrectly.
If it has maybe a link is missing but if it has been working ok previously maybe a faulty panel?
Yes something to do with temperature, the room thermostats start the process of operation with set temperatures, on more complex systems an Hi temp thermostat may prevent the system as a whole from working not just the manifold pump.

Click to expand...

Hmm ok.
It hasn't stopped working entirely. I check it every so often, and probably the pump is only running 25% of the time the heating is on.
When it's running the multimeter shows it's getting power, when it's not running the meter shows it is not.
But the valve will still be open and hot water running through the ufh pipes - just slowly of course!

davesparks said:

It's hard to tell from that picture, does the pump cable connect to a device attached to the manifold behind it?
It looks to me.like the type of system that uses a temperature operated switch in the manifold to control the pump, in which case its probably that temperature operated switch misbehaving.

Click to expand...

There's just a small wiring centre, with input from the thermostat - the live then goes into the manifold valve and then to the pump.

I could easily re-wire it so the pump comes on straight away as soon as the stat calls for heat, I just didn't want to do that without knowing if this was the intended design and risk causing problems. Not sure what could go wrong though...

AndyH83 said:

There's just a small wiring centre, with input from the thermostat - the live then goes into the manifold valve and then to the pump.

Click to expand...

Could you post a picture that shows the manifold valve and whatever is behind the pump in the original picture as it looks like the two white cables go downwards into something there.

How many zones are there on this UFH system? Or is it a simple single zone system?

AndyH83 said:

I could easily re-wire it so the pump comes on straight away as soon as the stat calls for heat,

Click to expand...

You talk of 'the' stat as if there is only one, so it may be possible to do so but if a multi zone system you cant connect to all stats. (Actually re-visited the photo and looks like pump output split with Y connector to 2 loops of same single zone!), so ok single zone.
This probably isnt a typical UFH control system with actuators etc, just a terminal box which a photo of (the internal contacts/terminals) might be useful.

AndyH83 said:

There's just a small wiring centre, with input from the thermostat - the live then goes into the manifold valve and then to the pump.

Click to expand...

As per Davesparks, it would be helpful to see a picture of the valve etc.
If the manifold valve referred to is a common or garden motorised 2-port, as found on S-plan heating systems etc, that could be the culprit.
They have a bit of a reputation (especially the 3-port) for the motor failing to operate the microswitch at the end of travel, thus not providing power to the subsequent circuit. Possible causes include stiff/sticky valve, weak motor, wear, microswitch etc.
Just a thought!