I cannot offer any suggestion; my UFH is around 15 years and never been flushed. When the gas guy was around earlier in the year to service the boiler, I did ask him and he said not necessary. Although I installed the UFH myself, he was the one to commission the system.

The UFH are ali lined pipes, all fittings are either brass or stainless and there is some copper pipe. As he told me, if there is no steel in the system, there will not be sludge.

But what do I know? However, I do notice that the actuator sight glass are slightly greenish, so assume there is some kinda 'growth' in the system

Posted By: RexI do notice that the actuator sight glass are slightly greenish, so assume there is some kinda 'growth' in the system

Could be, or is it possibly just corrosion of the copper pipe lengths?

What sort of water is put in UFH systems (I have no idea)? Does it get topped up or is it sealed?

Posted By: fostertom

Posted By: Simon Stilllow flow/low temperature

Those seem to be contradictory. If low flow, then delta t along each circuit must be high, otherwise tiny heat output.

Unless the pipe density is high enough to get the required heat output with low flow/low temp.

Posted By: Peter_in_HungaryUnless the pipe density is high enough to get the required heat output with low flow/low temp.

That doesn't go very far AIUI, to boost output. Once the pipes are at 100c/cs, the screed surface (or spreader plates) is very evenly, fully heated, with insignificant cooler stripes between the pipes - highly diminishing returns, to space the pipes closer.

Looking at it the other way, output is overwhelmingly locked to mean water temp, can only be slightly reduced by wider spacing, or majorly reduced by throttling its flow rate. So if mean water temp is 'low' then output is low - or even lower!

Posted By: Dominic Cooney

Posted By: Simon Stilltop floor

what sort of sytem is it? pipes with spreader plates? I did wonder if a pipe with a tightish bend at the end has finally kinked somewhere? I could imagine that happening with ours in the upstairs rooms, despite my best efforts when installing to try and prevent the chance of it. Just putting it out there as a possibility.

That's an interesting thought, but would only affect one of the loops - all of them have stopped showing any flow on that floor. (I had though initially it was just flowmeters stuck, but it's pretty clear now that water isn't circulating in those loops)

Posted By: GreenPaddyCould it be that there is air in the system? Upper floor ufh are more prone to that for obvious reasons. It does happen from time to time, even if there are auto air bleed valves fitted (which sometimes fail and leak or choke up with scale and fail to venthttps:///newforum/extensions/Vanillacons/smilies/standard/sad.gif" alt="" title="" >)

Likely need a booster pump by a plumber to give it a flush through, to push out air (just had this with a client last week coincidentally). That way you'll shift sludge and/or air. If you just request it to be done, rather than a load of man hours fault finding, it won't be so expensive. I'd put an antiflocculant in it (inhibitor not antifreeze obvs).

We did get air in the system for the first few years - it would get noisy after a while and we'd let the air out and add some water back. However - it eventually emerged that the reason for this was a very slow leak at one of the manifold connections (hidden behind a shelf next to the boiler). We found that, sorted the leaking joint, and have never had air or loss of pressure since.

I do wonder about air in conventional radiator systems - I suspect it's the result of small leaks that just arent noticed because they occur from the expansion/contraction process when the heating is used, but you've got enough heat to evaporate the leak. Whereas on UFH at sub 30C any expansion is going to be so minimal that's not going to happen.

As an aside we discovered a year ago that we'd had a very slight leak on the hot supply pipe to the kitchen sink (at the final connection). But the combination of the heat from the water and a low humidity warm house meant we only ever noticed it - as a flooded kitchen floor - when we were away for an extended period with the heating off. The rest of the time it had alway evaporated long before it reached the unit kickboards...
It happened two years running when we went away in winter. The first time we had a roofer out and 'improved' what we thought were the most at risk flat roof junctions where the leak might have emerged from....

Posted By: fostertomI see. Highly insulated. 29C, if that means flow temp, sounds right. But at that, your delta-t (difference between flow and return temp) must be really small - ideal for an ASHP - as your mean water temp must be a few degrees above your 20C room temp. You can only get that small delta-t if you have a highish flow rate. You have two pumps, so unless really tiny, two at 1/3 max could be quite powerful, between them. Any idea of the actual flow rate?

why do you only get the small delta if the flow rate is high? the house temperature is stable so once it's at equilibrium the return is never coming back below 20C and most of the time the flow is only a few degrees above that anyway.

How would I work out the flow rates - the pump for the upper floors has a max flow rate of 3m3 p/h (and is set to about 1/3 power)
the lower floor pump has a max flow rate of 5.7m3 and is set to power level 1 (of 3)