UFH running too hot

[johnrhug]

I am commissioning my Wunda UFH. All the flow rates have been set up as per the design.
No matter what I set the blender to the flow temperature rises to 50c and drops to 30c as the boiler cycles. In addition if I set the blender to minimum the flow rates on each circuit drop to below 1 L/m from 2.1 and 2.5.
With a remote thermometer the flow temp of the pipe from the boiler as it enters the manifold is about 48c. The 2 flows on each circuit are the same. It's as if the blender isn’t doing anything. The floor is getting above the recomended 27c.
Wunda Tech Support are going to send me a new blender but they say the recommendation for the pipes from the boiler are 15mm and I have 22mm. I'm only using 2 ports on a 4 port manifold with a combined UFH loop of 220 metres. They say this maybe overwhelming the manifold and I should replace the 22mm pipes with 15mm

Anybody else had this problem?

 

[Johntheo5]

What is the boiler minimum output and make/model?. even if averaging a dT of 10C and a flowrate of 2.0LPM per loop then the UFH demand is still only 2.8kW.
Is all the air purged from the manifolds?.

Is the manifold like shown below?.

 

[johnrhug]

Thank you for your reply.
The boiler is a Bosch Worcester CDi
I'm not sure what the minimum output is, where would I find that?
As far as I am aware there is no air in the system. I have run water through the loops until I no longer had air bubbles and there is no air coming out of the bleed valves.
The manifold is as shown in the attachment.

 

[SpecialK]

Are you measuring the temps in to the blender or at the manifold? I found the stick on fish tank temp gauges good for the manifold!

I had cycling problems with my boiler. I plumbed the bathroom radiator in to the UFH circuit which helped. Mine is a Vaillant and kept going in to shutdown as the internal bypass valve was operating causing the return temp to jump up too quickly. Can you feel the pipes to the boiler return? Are they getting hot?

What size is your boiler in kW?

 

[Johntheo5]

Thank you for your reply.
The boiler is a Bosch Worcester CDi
I'm not sure what the minimum output is, where would I find that?
As far as I am aware there is no air in the system. I have run water through the loops until I no longer had air bubbles and there is no air coming out of the bleed valves.
The manifold is as shown in the attachment.

The boiler label should be somewhere underneath it, with 25CD1, 30CD1, 37CD1 or 42CDi, which gives the output in kW but even the 25CDi may have a minimum output as high as 8.0kW or so.
If you have rads, suggest putting them in service for say 30 minutes or so (to get the boiler to fire continuously) with the UFH also on, set the boiler flowtemp to 55C and the UFH manifold to its minimum 30C? and see does the manifold flow(s) and flow/return temps remain steady, at least that might prove that the blender is working.

The combined UFH loop is 220M, is that ~ 110M/loop?.

 

[johnrhug]

I've got thermometers on the flow and return of the manifold. Also got a hand held thermometer. The temperature of the loops is the same as the flow from the boiler 48c no matter what I set the blender to.

The return pipe is getting warm,

Wunda say the 22mm feed from the boiier should be 15mm but I'm reluctant to change out the piping at this stage. I should have a new blender on Monday so will try that.

If I set the blender on minimum the flow meters on each loop drop from 2.5 and 2.1 down to 1.

 

[Johntheo5]

I've got thermometers on the flow and return of the manifold. Also got a hand held thermometer. The temperature of the loops is the same as the flow from the boiler 48c no matter what I set the blender to.

The return pipe is getting warm,

Wunda say the 22mm feed from the boiier should be 15mm but I'm reluctant to change out the piping at this stage. I should have a new blender on Monday so will try that.

If I set the blender on minimum the flow meters on each loop drop from 2.5 and 2.1 down to 1.

If the flowrate is falling to 1.0LPM/loop then the manifold pump might be on too low a setting to circulate the water through the loop, have a look at its setting, what dia piping is the UFH?.

 

[johnrhug]

The boiler label should be somewhere underneath it, with 25CD1, 30CD1, 37CD1 or 42CDi, which gives the output in kW but even the 25CDi may have a minimum output as high as 8.0kW or so.
If you have rads, suggest putting them in service for say 30 minutes or so (to get the boiler to fire continuously) with the UFH also on, set the boiler flowtemp to 55C and the UFH manifold to its minimum 30C? and see does the manifold flow(s) and flow/return temps remain steady, at least that might prove that the blender is working.

The combined UFH loop is 220M, is that ~ 110M/loop?.

Thanks Johntheo5,

I'm out at the moment so I'll check when I get back later today. I'll put the radiators on as suggested and see what the UFH temperatures are like then. I don't understand why the blender is letting the water temperature get so high. It appears to be passing all the heat from the boiler through to the loops.

220m is the total of both loops, one is 120 the other 100.

 

[Johntheo5]

Presume boiler flow/return piping to manifold connected correctly?, the blender does seem to be moving a least manually since the flowrates change even though they shouldn't, the TMV shuttle should throttle off one side flow and increase the other side depending on mixing requirements.

 

[johnrhug]

If the flowrate is falling to 1.0LPM/loop then the manifold pump might be on too low a setting to circulate the water through the loop, have a look at its setting, what dia piping is the UFH?.

The loops are 16mm

 

[Johntheo5]

Something a bit strange there.
120M, say 144M (allowing 20% more for bends etc) of 16mm (12mm ID) "plastic" piping has a friction loss of 2.85, say 3.0M at a flowrate of 2.5LPM so the pump only requires a head of 3.0M at a total flowrate of 5.0LPM which any 6M manifold pump should give on fixed speed 3, only 1.88M head is required at 2.0LPM/loop.
The pipe friction loss at 1.0LPM/loop is only 0.52M

 

[Johntheo5]

This is a fairly typical example of how a TMV works, its far easier for the shuttle to jam/stay in the cold position as the spring pushes the shuttle to open the hot side port and close the cold side port, the hydraulic piston can exert tremendous force to close off the hot side port so far more likely to jam in the cold position due to a sticking shuttle in the valve body O ring.

 

[johnrhug]

Thanks everyone for your suggestions. Lots for ne to try, plus a replacement blender valve has arrived. She who must be obeyed has decreed no more UFH work until Monday. I'll provide an update on progress next week

 

[Johntheo5]

If you wish, you can do a few tests on that new blender valve, turn it to minimum and pour some cold water into the mixed outlet, water should exit from the hot port?, increase the water temp to a few degrees above the minimum setting and see if no water comes from the hot port now.
Also, have a look through this thread.

UFH blending valve blending too hot

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...

www.diynot.com

 

[dilalio]

Check those flow and returns from the boiler are correct into the manifold.