Am I right in this train of thought? Daikin LT with UFH

Hi everyone.

Wonder if someone might be able to help. I have a Daikin LT system, with UFH, and also attached to solar.

So, firstly, the system constantly loses pressure. My HA send engineers, and they just turn a knob and the pressure comes back up to 2 bar on the manifold. However, I have noticed black stuff on the floor underneath the pipes where the boiler is. Engineer suggests it is Iron Oxide, which is the by product of a pipework leak somewhere. Am i right in thinking this could be the cause of the pressure drop?

Secondly ( re the UFH), the manifold is a 9 port one, and 1 of the circuits is 100m long (M1), and the other is 88m long (M2). When all the circuits are open (for the whole house), and calling for heat, M1 and M2 only have less than 1 litre per min going into them. Yet another circuit of only 14 m has 3litres per min going in! Another circuit of 30 m, has 2 litres per min going in! I think you might able to teell where this is going. Am i right in thnking that if there is inadequate flow to the circuits, it will take longer to reach temp (if at all?) And of course, be costing money all the time it is trying to reach temp?

From my investigations, the 100m circuit should have 2.5 litres per min, and the 88m circuit should have 2.2litres per min. (I'm taking the pipe length and dividing by 40 ) Am i correct with these calcs?

Moving on, the flow rate problem was explained to the engineer, who merely removed the actuators, and told me to "see how I got on" Well of course all this did, was remove my ability to control that circuit from the thermostat. So I put them back on. Maybe the engineer doesnt have an energy crisis in his town! Even with the actuators removed, the flow rate indicators, still showed less than 1l/p/min

The next engineer came, and said he needed to check the flow and return rate. Flow is 34, return is 25. How is the flow and return rate even relevant to this problem ?? This engineer suggested that the black iron oxide may have got into the UFH circuits, and be preventing the flow rate. I think this is entirely possible, but if someone could confirm?

Finally, I have the flow rates that the original installer set. All at 1.6litres per min. How can this be correct when the longest circuit is 100m, and the shortest is 14m.

I look forward to you comments to help me with my response to the HA. I am totally un convinced that their contractors have a scooby doo!

Thankyou in advance!

Just my daft thoughts (In red​) but maybe itll be helpfull. Or maybe someone that knows what there talking about will reply.

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Originally Posted by cathyr456

Hi everyone.

Wonder if someone might be able to help. I have a Daikin LT system, with UFH, and also attached to solar.

So, firstly, the system constantly loses pressure. My HA send engineers, and they just turn a knob and the pressure comes back up to 2 bar on the manifold. However, I have noticed black stuff on the floor underneath the pipes where the boiler is. Engineer suggests it is Iron Oxide, which is the by product of a pipework leak somewhere. Am i right in thinking this could be the cause of the pressure drop? Normally pressure drops come from having a leak, or an increase in the volume of the system. Is there iron/steel parts you could check around for leaks?

Secondly ( re the UFH), the manifold is a 9 port one, and 1 of the circuits is 100m long (M1), and the other is 88m long (M2). When all the circuits are open (for the whole house), and calling for heat, M1 and M2 only have less than 1 litre per min going into them. Yet another circuit of only 14 m has 3litres per min going in! Another circuit of 30 m, has 2 litres per min going in! I think you might able to teell where this is going. Am i right in thnking that if there is inadequate flow to the circuits, it will take longer to reach temp (if at all?) And of course, be costing money all the time it is trying to reach temp? The longer circuits will have greater resistance to flow. Its probably going to give poor heating to the rooms on the longer circuits, and have warmer than expected return temps on the shorter circuits.

From my investigations, the 100m circuit should have 2.5 litres per min, and the 88m circuit should have 2.2litres per min. (I'm taking the pipe length and dividing by 40 ) Am i correct with these calcs? Not sure what calcs your on about.

Moving on, the flow rate problem was explained to the engineer, who merely removed the actuators, and told me to "see how I got on" Well of course all this did, was remove my ability to control that circuit from the thermostat. So I put them back on. Maybe the engineer doesnt have an energy crisis in his town! Even with the actuators removed, the flow rate indicators, still showed less than 1l/p/min I'm guessing you need to adjust the flows for all the circuits, if youve got a short circuit with less restriction then its going to be easier to push water through it at a higher rate.

The next engineer came, and said he needed to check the flow and return rate. Flow is 34, return is 25. How is the flow and return rate even relevant to this problem ?? This engineer suggested that the black iron oxide may have got into the UFH circuits, and be preventing the flow rate. I think this is entirely possible, but if someone could confirm? Flow and return rate? Im guessing you mean temperature out to the circuit and temp of return from the circuit. If theres something in the system other than water, it could build up and cause a restriction, it could also coat the inside surface and give poorer heat transfer. But from what Ive come across, the insides of pipework are unlikely to be perfect.

Finally, I have the flow rates that the original installer set. All at 1.6litres per min. How can this be correct when the longest circuit is 100m, and the shortest is 14m. If all the ciruits have roughly the same amout of heating requirement, then there all going to have a similar flow rate. Pressure to get that flow rate through different length ciruits is likely to be different though.

I look forward to you comments to help me with my response to the HA. I am totally un convinced that their contractors have a scooby doo! Try a differnt one?

Thankyou in advance!

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to calculate flow rate for heating loop = loop length divided by 40 =flow rate
the system will have been filled with heat transfer fluid that is also a antifreeze and has inhibiters for corrosion ect if you keep filling with water from the filling loop this will make it weak and might cause a problem in the water freezing if you keep having to top up the system must have a leek

when the heating loops close a pressure bypass will start to open to keep the flow rate correct for the heat pump
depending how the controls have been set up and how well insulated you house is will affect the running cost also ASHP are not very efficient in cold weather

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stains under the boiler are probably from a leaking pressure release valve... normally a little red spring loaded valve

I googled for a pick for you but here's a video instead

https://www.youtube.com/watch?v=uWg_lySYjU8

sometimes they don't seal properly after they've released excess pressure... if you turn the knob a bit so some water comes out then let it snap shut quick it might re-seal it again (worth a try)

there should be some inhibitor in the system to stop corrosion (the black stuff) - you can still get a bit of black stuff with inhibitor in tho

there should be adjustment valves on the under floor heating manifold to control the pressure of each loop... turn down the fastest loops - as they come down the slower loops should come up - make sure you've got all zones turned on when you do this


are you calling out heat pump/refrigeration engineers? you need a plumber/heating engineer instead, a decent one should be able to sort this for you in no time.

if the system is blocked/silted up they can do a power flush - they connect a pump to the system and pump cleaning chemicals through fast to flush it all out

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Originally Posted by martinw58

to calculate flow rate for heating loop = loop length divided by 40 =flow rate

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Can you explain this because flow rate is as far as I see it not determined by loop length?
So I diagree somehow with this rough calculation altough it will be a good starting point.
Flow rate is calculated by the heating capacity of the area the considered pipe spans and an assummed DT of 5K over the waterflow.
You need a regulation where all the circuits comes finally to the same DT.
https://www.itap.it/wp-content/uploads/Sizing_EN.pdf