UFH blending valve blending too hot

[deadfire19]

I have installed a UFH manifold with one 60m 12mm loop and the flow to the UFH loop is too hot.

The flow into the manifold is 36C and the return is 32C. I'm planning to put an engineered wood floor on top of the ufh so my maximum flow temp must be 27C or I'll risk damaging the floor.

Im using the Reliance 3/4"-1" UFH Thermoguard Blending valve in front of the manifold and it's set to minimum, which should be 26C. The flow into the manifold is from the radiator circuit and its plumbed in with a 22mm flow and return. The boiler is set to 65C (since the water tank needs to reach that temp).

Why is my blending valve not working as intended?

Any help would be massively appreciated.

 

[Johntheo5]

One loop if flowing say 3LPM at a dT of 4C will omly emit 0.8kw with a manifold hot (65C) flow of 0.35LPM mixing with 2.52LPM at 32C to give a mixed flow of 2.87LPM at 36C, these are tiny flowrates, especially the hot flowrate of 0.35LPM, don't know how tight flow controls the TMV can give, reliance can maybe suggest a more suitable capacity TMV.

What is the maximum floor temperature allowed?.

 

[deadfire19]

One loop if flowing say 3LPM at a dT of 4C will omly emit 0.8kw with a manifold hot (65C) flow of 0.35LPM mixing with 2.52LPM at 32C to give a mixed flow of 2.87LPM at 36C, these are tiny flowrates, especially the hot flowrate of 0.35LPM, don't know how tight flow controls the TMV can give, reliance can maybe suggest a more suitable capacity TMV.

What is the maximum floor temperature allowed?.

The maximum floor temperature allowed will be 27C (this is coming from both my floor manufacturer and the instruction manual for the reliance blending valve).

I'm happy to increase the flow rate or wait to use the UFH until more loops are added, but even when fully populated, the manifold might shut all but one zone down and that zone might be a tiny ensuite. It still shouldn't overheat the floor in that case. Right?

 

[Johntheo5]

True enough, I'd love to see the inside of one of those TMVs, don't know how tight shut off, I imagine the valve is spring loaded to be fully open to admit hot water when cold and then throttle down the hot when reaching the required flow temperature? Practically speaking, if handy yourself, you could just remove the TMV and just pour some hot water into the mixed outlet port and ensure not a drop of water comes out of the hot inlet port, if you do remove it blow through the various ports to see which way its biased, also you might just find a bit of debris in it preventing proper operation after dissassembling it.

What is the flowmeter (if installed) reading?.

 

[deadfire19]

True enough, I'd love to see the inside of one of those TMVs, don't know how tight shut off, I imagine the valve is spring loaded to be fully open to admit hot water when cold and then throttle down the hot when reaching the required flow temperature? Practically speaking, if handy yourself, you could just remove the TMV and just pour some hot water into the mixed outlet port and ensure not a drop of water comes out of the hot inlet port, if you do remove it blow through the various ports to see which way its biased, also you might just find a bit of debris in it preventing proper operation after dissassembling it.

What is the flowmeter (if installed) reading?.

The flow meter is reading 1.5l/m

The pump at full tilt can do 2.5l/m but I'm running it at it's lowest setting with some restriction at the flow adjuster.

There's a diagram of the blending valve in the manual. But I don't want to drain my CH system only to need to do it again to replace the valve completely a few days later, I'm wondering if there is anything wrong with my setup or if the blending valve is faulty before draining the CH.

I should have added isolaters in front of the blending valve in hindsight but that wasn't the recommended installation in the manual.

 

[Johntheo5]

That manifold pump will pump 25/35LPM at least, I would increase the flow rate straight away with the flow adjuster to at least 3LPM, the present flowrate of 1.5LPM at a dT of 4C only gives a output of 0.42kw with a hot water flowrate of 0.14LPM (fairly tight control), I would keep increasing the flowrate and you may well find that the manifold temperature decreases.

 

[deadfire19]

The pump won't do more than 2L/m on setting 1 and on setting 3 it does 2.5L/min.

Perhaps the reason is that it's 12mm tubing which is on the thinner end for ufh.

I still don't understand why the blending valve doesn't turn the supply from the CH off if both the return from the UFH and the CH in are over the set temperature.

The pipe from the CH is still extremely hot to the touch, so it must be getting some decent flow rate from the CH.

 

[Johntheo5]

I suppose the 60m of 12mm piping is causing a big pressure loss, so I take it that the flow regulator is full open with the pump setting on 3, to give 2.5LPM, has this decreased the manifold temperature?. and what is the UFH flow/return now at 2.5LPM?.

 

[deadfire19]

The delta is roughly the same no matter the flow rate, (2 v 2.5L/min) it seems to be dependent more on the flow temp (the higher it is the bigger the delta).

The numbers are fluctuating depending on whether the boiler is on or off.

I did notice that as soon as you bump the pump speed up, the temp on the inlet jumps

 

[Johntheo5]

If you are running the UFH on its own then the boiler must be cycling rapidly?, most, if gas, boilers will not run continuously at less than ~ 5kw heat demand, any idea of the hot water supply head?, (does the system have a LLH with secondary pump(s) ), the higher this is the more the TMV shuttle has to throttle to restrict the HW flow to the very low required flowrate, maybe, temporarily, ensure the boiler is running continuously with sufficient heating load from the rads and keep reducing the boiler flowtemp to see if the manifold flowtemp gets down to 27C?

What boiler do you have?

 

[deadfire19]

It's a valiant 618 plus (18kw).

There's a "always on" radiator in the loop and a bypass between the flow and return directly under the radiator.

I did notice I had some cold radiators after the change so I've opened them up fully in the meantime. All the radiators are on Tado thermostats (except the always on one).

Unfortunately it's still 36C flow 34C return on the UFH

 

[Johntheo5]

Under those conditions, the UFH is emitting 0.35kw and the HW flowrate is 0.16LPM, assuming that this is the lowest achievable flowrate then reducing the boiler flowtemp to even 60C theoretically at any rate, should give ~ manifold flowtemp of 27C, can you try this, or keep reducing it until you achieve that 27C, you can read off the boiler flowtemp in parameter d.40 or d.040, I think.

 

[deadfire19]

TLDR; take the plastic cap off and manually adjust clockwise.

Thanks for all of the help throughout.

I took the plunge today, emptied the CH and took apart the valve, wiped it clean with kitchen towel, reapplied some silicone WD-40 as suggested by the manual, put it back together and it works. Flow of 27C, Return of 25C. The CH is running at a flow of 65C.

For anyone coming across this issue in the future, before you do this whole procedure. Take the cap off the blending valve and keep twisting clockwise past what the cap would allow you. You will feel the spring bottom out. This is your new minimum. The calibration of mine from the factory must have been wrong.

The commisioning instructions are terrible, they do not mention that the valve under the plastic cap has a lot more adjustment than what the plastic cap allows. That being said I would NOT risk twisting it anticlockwise since the adjustment thread (might) unscrew completely and with the pressure of the water in your pipes you'll have a mess.

 

[Johntheo5]

That,s great that you are sorted out.

You say you twist clockwise after removing the cap, the cap is turned anticlockwise to increase the temp (at least + is shown in a anticlock direction) so assume this is increasing the spring tension? Read somewhere where someone had a problem where no HW would flow until he backed off the adjustment to let some HW leak past but this doesn't seem very logical as I assume that the TMV is calling for full HW when cold?.

 

[deadfire19]

That,s great that you are sorted out.

You say you twist clockwise after removing the cap, the cap is turned anticlockwise to increase the temp (at least + is shown in a anticlock direction) so assume this is increasing the spring tension? Read somewhere where someone had a problem where no HW would flow until he backed off the adjustment to let some HW leak past but this doesn't seem very logical as I assume that the TMV is calling for full HW when cold?.

Twisting the knob moves the whole assembly of the piston in or out (its on a thread).

There is a piston in the threaded head that pushes down on the spring the hotter it gets and comes up when it gets cold.