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Advice required for the correct settings for UFH


ChantalA
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Desperate Advice Required!.

My current set up is:

1. A 24w combi condensing boiler

2. 150Lts buffer tank.

3.Google Nest Thermostat

 

The UFH pump is connected direct to the buffer tank, and the controller in the tank is linked to the pump and  is set to only pump water around the system when the water in the tank is at 40 degrees.

The boiler itself, when heating is being called by the Nest is set to 60 degrees.

There is no mixer value installed currently.

 

Firstly, is this a correct set up?

Secondly the problem is, this set up means that the boiler is continually running and our gas consumption is huge, approximately 35 kgs over 3 days; and also,  when the temperatures outside at 1/2 degrees or lower,  the system really struggles to heat the house up to 20.5 degrees. The tank never seems to heat to more than 45 degrees despite 60% water being added to it, unless the UFH is switched off completely. 

 

Can someone please explain the need for the buffer tank and whether it is better to have this than have the UFH connected direct to the boiler, which can then be set at 40 degrees for the UFH.

Also do I need a mixer valve fitted in the system somewhere?

 

I look forward to any advice.

Thank you....

Chantal, a complete beginner when it comes to UFH systems!

 

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Can you post a picture of the UFH manifolds including close ups of any valves dials or controls?

 

Is this bottled gas as you are using the unusual measure of Kg of gas used?

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18 minutes ago, ChantalA said:

There is no mixer value installed currently.


Issue #1

 

19 minutes ago, ChantalA said:

only pump water around the system when the water in the tank is at 40 degrees.


Issue #2

 

I would hazard a guess that the tank stat is a bimetallic one so has around a +/-3°C hysteresis so is randomly switching on an off. The tank will get to 60°C very slowly, and I would also suggest that the tank stat control is your first issue. 
 

Questions -

— who installed it ..?

— is the buffer direct or indirect plumbed ..? Does it have a coil (photo of the buffer will help)

 

23 minutes ago, ChantalA said:

it is better to have this than have the UFH connected direct to the boiler, which can then be set at 40 degrees for the UFH.

 
Categorically no, and you won’t get a boiler to run that low, it won’t condense and your gas usage will go up not down !

 

 

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Not sure what you mean by " despite 60% water being added to it"

 

So, boiler is trying to heat water in cylinder to 60 degrees, but when it gets to 40 deg you are pumping the water away to the UFH.  The pump from your boiler and the UFH are possibly the same size.  So the heat given to the cylinder is being extracted, by the UFH pump, as quick as it can be delivered.

 

You are possibly lucky the system is not heating up, as you could be delivering 60 deg water into your floor, which would not be good.

 

More once you clarify the point asked for above.

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Hi Guys, Thanks for your quick response.

SO in answer to your queries.

 

ProDave, my manifolds aren't easy to access, but i can tell you that they are straight tubes in and out with the floor pipes attached,there are absolutely no valves dials or controls except the flow rate ones, so I can't tell what the temp is at the input and output stages. I am on bottled gas ?

 

PeterW, no idea who installed it... but the buffer is direct plumbed to the boiler and has a coil inside. it is a closed circuit between the two.

JohnMo - 60% water being added to it probably shows my ignorance here... I meant pushed through from the boiler to the coil to heat the water up, sorry! I also think the pump to UFH is more powerful than the pump in the boiler..

Hope these help...

So in this scenario would a mixer value help in the mix... perhaps removing the buffer, adding a mixer value, have the boiler running at the optimum which I believe is 56 degrees with a mixer value keeping the water temp through the UFH at a constant 40 degrees? If the buffer tank wont ever get to temp because it is being drained by the UFH pump, the boiler is going to be running constantly hence the gas consumption... or have I got this all totally wrong???

 

Cheers

Chantal

 

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54 minutes ago, JohnMo said:

Not sure what you mean by " despite 60% water being added to it"

 

So, boiler is trying to heat water in cylinder to 60 degrees, but when it gets to 40 deg you are pumping the water away to the UFH.  The pump from your boiler and the UFH are possibly the same size.  So the heat given to the cylinder is being extracted, by the UFH pump, as quick as it can be delivered.

 

You are possibly lucky the system is not heating up, as you could be delivering 60 deg water into your floor, which would not be good.

 

More once you clarify the point asked for above.

 

Sorry - 60% water being added to it probably shows my ignorance here... I meant pushed through from the boiler to the coil to heat the water up, sorry! I also think the pump to UFH is more powerful than the pump in the boiler..

Hope these help...

So in this scenario would a mixer value help in the mix... perhaps removing the buffer, adding a mixer value, have the boiler running at the optimum which I believe is 56 degrees with a mixer value keeping the water temp through the UFH at a constant 40 degrees? If the buffer tank wont ever get to temp because it is being drained by the UFH pump, the boiler is going to be running constantly hence the gas consumption... or have I got this all totally wrong???

 

Cheers

Chantal

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1 hour ago, PeterW said:


Issue #1

 


Issue #2

 

I would hazard a guess that the tank stat is a bimetallic one so has around a +/-3°C hysteresis so is randomly switching on an off. The tank will get to 60°C very slowly, and I would also suggest that the tank stat control is your first issue. 
 

Questions -

— who installed it ..?

— is the buffer direct or indirect plumbed ..? Does it have a coil (photo of the buffer will help)

 

 
Categorically no, and you won’t get a boiler to run that low, it won’t condense and your gas usage will go up not down !

 

 

no idea who installed it... but the buffer is direct plumbed to the boiler and has a coil inside. it is a closed circuit between the two.
 

So in this scenario would a mixer value help in the mix... perhaps removing the buffer, adding a mixer value, have the boiler running at the optimum which I believe is 56 degrees with a mixer value keeping the water temp through the UFH at a constant 40 degrees? If the buffer tank wont ever get to temp because it is being drained by the UFH pump, the boiler is going to be running constantly hence the gas consumption... or have I got this all totally wrong???

 

Cheers

Chantal

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1 hour ago, ProDave said:

Can you post a picture of the UFH manifolds including close ups of any valves dials or controls?

 

Is this bottled gas as you are using the unusual measure of Kg of gas used?

my manifolds aren't easy to access, but i can tell you that they are straight tubes in and out with the floor pipes attached,there are absolutely no valves dials or controls except the flow rate ones, so I can't tell what the temp is at the input and output stages. I am on bottled gas ?

 

The buffer is direct plumbed to the boiler and has a coil inside. it is a closed circuit between the two. I also think the pump to UFH is more powerful than the pump in the boiler..
 

So in this scenario would a mixer value help in the mix... perhaps removing the buffer, adding a mixer value, have the boiler running at the optimum which I believe is 56 degrees with a mixer value keeping the water temp through the UFH at a constant 40 degrees? If the buffer tank wont ever get to temp because it is being drained by the UFH pump, the boiler is going to be running constantly hence the gas consumption... or have I got this all totally wrong???

 

Cheers

Chantal

 

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Re gas consumption.  Simple laws of physics, if the boiler is burning and heating water it must be going somewhere.  If the house is only just reaching your target temperature, then it won't be wasting massive amounts of gas.  There are probably some savings to be had by optimising temperatures and improving efficiency, but probably not massive savings.

 

What it the context here?  Old house? New house, have you just bought it and this was what the previous owner had etc etc.

 

Frankly bottled gas would be my last choice for heating, an oil boiler would have been a better bet perhaps?

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So my setup is similar to yours. My insulation levels are very high, and the UFH is in thick concrete so mine will respond differently to others.

 

This is how mine is connected.

Boiler to coil in cylinder.  Cylinder contents connected to UFH.  But my pump is at the UFH manifold and has temperature mixing valve also.

 

Controls.

Thermostat, wired to a two port valve on the UFH supply from the cylinder.  The micro-switch contacts in the two port valve, give a volt free call for heat to boiler, this signal goes through the cylinder thermostat.

 

My settings are, boiler fires at 50 degrees, the cylinder thermostat is set at 40 degrees, UFH manifold regulating valve set at 34 degrees.  Thermostat is half way up cylinder, so expect top of cylinder is close to 50 degrees.

 

Operation

Thermostat calls for heat, two port valve opens, if cylinder is below 40 degs, boiler fires, if at 40 degrees boiler does not fire.  Boiler runs until cylinder thermostat gets to 40 degs.  If thermostat is still calling for heat and cylinder goes below 37 degrees, boiler fires.

 

I run the UFH pump 24/7.

 

Setting up temperatures.

Set thermostat at desired temp.

The flow temp through the UFH is determined by the following.

Doesn't get to temp, flow temp increase.

Temperature overshoots, turndown flow temperature.

Leave 24 hours between fiddling with temperature.

 

 

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17 minutes ago, JohnMo said:

So my setup is similar to yours. My insulation levels are very high, and the UFH is in thick concrete so mine will respond differently to others.

 

This is how mine is connected.

Boiler to coil in cylinder.  Cylinder contents connected to UFH.  But my pump is at the UFH manifold and has temperature mixing valve also.

 

Controls.

Thermostat, wired to a two port valve on the UFH supply from the cylinder.  The micro-switch contacts in the two port valve, give a volt free call for heat to boiler, this signal goes through the cylinder thermostat.

 

My settings are, boiler fires at 50 degrees, the cylinder thermostat is set at 40 degrees, UFH manifold regulating valve set at 34 degrees.  Thermostat is half way up cylinder, so expect top of cylinder is close to 50 degrees.

 

Operation

Thermostat calls for heat, two port valve opens, if cylinder is below 40 degs, boiler fires, if at 40 degrees boiler does not fire.  Boiler runs until cylinder thermostat gets to 40 degs.  If thermostat is still calling for heat and cylinder goes below 37 degrees, boiler fires.

 

I run the UFH pump 24/7.

 

Setting up temperatures.

Set thermostat at desired temp.

The flow temp through the UFH is determined by the following.

Doesn't get to temp, flow temp increase.

Temperature overshoots, turndown flow temperature.

Leave 24 hours between fiddling with temperature.

 

 

Thanks John,  the real big difference is that your thermostat is wired to your 2 port valve on the UFH supply from the cylinder, not to the boiler, which makes a lot more sense to me! the question now is whether i can do that with a google nest!

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3 hours ago, ChantalA said:

The UFH pump is connected direct to the buffer tank, and the controller in the tank is linked to the pump and  is set to only pump water around the system when the water in the tank is at 40 degrees.

The boiler itself, when heating is being called by the Nest is set to 60 degrees.

There is no mixer value installed currently.

 

I think that's OK but it's different to how many systems work...

 

Many would have the Nest control the pump between buffer and UFH.

Then the stat on the buffer would control the boiler, firing up the boiler when the buffer goes below the set temperature.

 

That's how my TS system works. The down side is the tank is always kept at the set temperature even if the UFH is off. You can add a timeclock to fix that.

 

 

 

 

 

 

 

 

Edited by Temp
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2 hours ago, ChantalA said:

So in this scenario would a mixer value help in the mix... perhaps removing the buffer, adding a mixer value, have the boiler running at the optimum which I believe is 56 degrees with a mixer value keeping the water temp through the UFH at a constant 40 degrees? If the buffer tank wont ever get to temp because it is being drained by the UFH pump, the boiler is going to be running constantly hence the gas consumption... or have I got this all totally wrong???


Ok so the hydraulic separation is pointless here - the boiler is short cycling and costing you more as it isn’t getting the heat into the tank and it needs to be replumbed. 
 

@joe90 has just had a near identical issue with buffer and mixer / manifold etc but in your instance the wiring is wrong. The Nest should be controlling the UFH pump, and the cylinder stat should control the boiler. The way it is wired currently the boiler stat is what is controlling the flow and I’ve no idea who has come up with the 40°C idea but that’s just wrong on every level … 

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8 minutes ago, PeterW said:


Ok so the hydraulic separation is pointless here - the boiler is short cycling and costing you more as it isn’t getting the heat into the tank and it needs to be replumbed. 
 

@joe90 has just had a near identical issue with buffer and mixer / manifold 

Not sure I really agree.

 

There is no short cycling, the boiler is running constantly, as stated in the original post.

 

Joe90 had a mixer valve, this system does not.  Even when he replumbed he still had issues, because of issues with valves in the manifold.

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Indeed I did, the coil was not transferring enough heat into the buffer, but it was heated by an ASHP which tends to heat at a cooler temp. I abandoned the coil and made it direct and with a decent mixer it now works much better ?(thanks to @PeterW).

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8 minutes ago, JohnMo said:

There is no short cycling, the boiler is running constantly, as stated in the original post.


That’s could well be short cycling. 
 

Unless you sit and watch it and time it, then the boiler “running constantly” could well be the pump overrun or similar that happens with a lot of condensing boilers. The stat will cut the burners and the pump continues, the burner then restarts and it cycles all over again. 
 

Without being spanner’s on to this it is difficult to diagnose but for me the buffer needs to be whole circuit, the tank stat needs to control the boiler (as per @Temp) and the nest needs to control the UFH pump and it all needs to be blended. 

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Don't disagree that it need blending. 

 

With a 150 l cylinder the gas boiler has plenty to work on, so don't understand why it would short cycle, unless it has a super small coil.  Mine does not short cycle, set up exactly the same as far as cylinder and boiler.  Are you saying every uvc or thermal store on gas boiler short cycles?  Hydraulically it's the same.

 

Easy way to sort out, is for Chantal, to keep an eye on the CH flow temp at the boiler.  Flow temp should be a steady 60 degree over about 5 to 10 mins.  If it is, it's not short cycling.  If it does go up and down the a replumb may be needed.

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1 hour ago, JohnMo said:

Joe90 had a mixer valve, this system does not.  Even when he replumbed he still had issues, because of issues with valves in the manifold.

It was a duff designed bypass built into the manifold that caused the problem. Blanking it off and installing a “proper” temp mixing valve sorted it ( after I balanced the two pumps etc).yes a decent mixing valve is essential IMO.

Edited by joe90
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2 hours ago, PeterW said:


Ok so the hydraulic separation is pointless here - the boiler is short cycling and costing you more as it isn’t getting the heat into the tank and it needs to be replumbed. 
 

@joe90 has just had a near identical issue with buffer and mixer / manifold etc but in your instance the wiring is wrong. The Nest should be controlling the UFH pump, and the cylinder stat should control the boiler. The way it is wired currently the boiler stat is what is controlling the flow and I’ve no idea who has come up with the 40°C idea but that’s just wrong on every level … 

Hi Peter, so how do you wire the nest to control the UFH Pump, do you need some special valve? Thanks

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Just now, ChantalA said:

Hi Peter, so how do you wire the nest to control the UFH Pump, do you need some special valve? Thanks

 

2 hours ago, PeterW said:


Ok so the hydraulic separation is pointless here - the boiler is short cycling and costing you more as it isn’t getting the heat into the tank and it needs to be replumbed. 
 

@joe90 has just had a near identical issue with buffer and mixer / manifold etc but in your instance the wiring is wrong. The Nest should be controlling the UFH pump, and the cylinder stat should control the boiler. The way it is wired currently the boiler stat is what is controlling the flow and I’ve no idea who has come up with the 40°C idea but that’s just wrong on every level … 

Also where in the system should the mixer valve be installed. It is clear the system needs one!

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Mixer wants to be after the buffer but before the pump. So it can either go at the manifold or at the buffer end, wherever you’ve got more room. 
 

Nest wiring depends on how it is wired and where the Nest Heatlink unit is - they come with a set of instructions but if it’s the single channel one from memory you wire the pump neutral to the base neutral and then there are 3 connections for switching and it’s live to common then out to the pump from switched live. Without seeing which one it is I would be guessing though. 
 

sorting this is a couple of hours for a decent plumber, not difficult to resolve. 

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On 21/01/2022 at 23:48, PeterW said:

Mixer wants to be after the buffer but before the pump. So it can either go at the manifold or at the buffer end, wherever you’ve got more room. 
 

Nest wiring depends on how it is wired and where the Nest Heatlink unit is - they come with a set of instructions but if it’s the single channel one from memory you wire the pump neutral to the base neutral and then there are 3 connections for switching and it’s live to common then out to the pump from switched live. Without seeing which one it is I would be guessing though. 
 

sorting this is a couple of hours for a decent plumber, not difficult to resolve. 

thank you,will let you know how it goes once sorted. !

 

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