underfloor heating

[ivanm]

hi there
i have just moved into a new house with underfloor heating, water not electric, the problem is that it does not appear to be working properly as it has been off for about 4 months, you can hear the pumps working etc, but the floor only heats up in patches rather than a constant heat across all the floors, do they need bleeding and if so how do you do that
look forward to comments please
Ivanm

 

[croydoncorgi]

You may get some air out of bleed screws on the U/F manifolds.

But it might be easier to just let it run for a while, so that the air works its way out into the Return and then out of the system via the ABV in the boiler. Note that most U/F systems have a mixing valve with a thermostat to set the floor temperature (which should be a LOT lower than the likely Flow from the boiler: ie. 45 degrees or so, max). When the water being circulated in the floor reaches the mixing valve temperature setpoint, any air in the floor piping will just circulate through the floor, mixing valve and pump and back into the floor.

A way to get the air out is to leave the floor circulator AND the main CH pump running with the boiler OFF. That way, cold water from the rest of the CH system will be pushed into the U/F system and should carry the air out, back to the boiler. In summer, that should not pose a problem.

 

[Agile]

I am guessing that this may be a brand new house.

If so then John is possibly being over optimistic that it was ever balanced at all.

It is really a specialist heating engineer task but you might be able to do it yourself if you get a digital contact thermometer.

Its better to wait until you need heating as it takes a while to get it stabilised, say at least an hour.

You measure the return temperature on each loop and then increase the flow in the coolest and reduce the flow in the hotest to balance then to the same temperature differential. Opinions vary but a drop of about 5-10 degrees is typical.

Then you wait another hour for it to stabilise and see what change you have achieved. The closer to balance the smaller the change to make.

Many of the adjustment valves have a scale which give helps to give an idea. It may help to note the starting positions.

Tony

 

[croydoncorgi]

My mistake- I mistakenly thought that you KNEW the U/F system had air in it...

If it's 'patchy' in large patches, then Tony is probably right that the flowthrough individual loops has not beenadjusted properly. Depending on the make of manifold, there may be sight-glasses with flow-meters inside. Follow manufacturer's guidelines to adjust the flow in each area of floor.

 

[ivanm]

My mistake- I mistakenly thought that you KNEW the U/F system had air in it...

If it's 'patchy' in large patches, then Tony is probably right that the flowthrough individual loops has not beenadjusted properly. Depending on the make of manifold, there may be sight-glasses with flow-meters inside. Follow manufacturer's guidelines to adjust the flow in each area of floor.

thanks for all your comments,one other question is, if it has not been run for a while how long should it take to warm the floor, the house has undefloor heating downstairs with rads upstairs, the upstair rads came on imediatly and provided lots of heat, the undefloor heating however took at least an hour and then as above was patchy
Ivanm

 

[croydoncorgi]

Depends on the floor material, covering, etc.
U/F is DIFFERENT- everything is meant to happen slowly and at low temperatures, so timings on your programmer need to allow for this. Warming up a floor from cold SHOULD take several hours - otherwise the mixing valve(s) is/are probably set too hot. Patchy heat suggests either air in the matrix or lack of flow, or both.