How is it controlled? And why does it need to come on in the middle of the night? Just rehashed a local house with 2 rad zones, 2 UFH zones and HWS. Boiler only fires and pumps only come on when timeclocks AND zone/cylinder thermostats are calling.
Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws
So I have both timers and thermostatic controls. In this case the UFH came on because the temperature dropped overnight - so it kicked in the heating.
I would have thought only the room/s calling for heat shold be getting it, and looking at the photo it would appear that the boiler would come on, quickly heat up the small quantity of water in the LLH and local pipes and shut down. If it is coming on for longer periods and using excessive gas it could be due to unwanted circulation through other circuits, perhaps a motorised valve stuck open or one of the circuits off the manifold not shutting down (or even crossed wires!). I suppose you could wait until everything is timed off and cooled down then override one of the rooms on UFH and see what circuits get warm?
Thanks for the reply! Check all the motorised valves / been watching all the pumps going on and off carefully - so far have not found anything untoward.
My only theory now is with the UFH that the effect of the mixing valve at 50 degrees is somehow distorting the temperature inside the header - such that the boiler thinks it needs to keep firing even though there is sufficient hot water flowing in the UFH circuit.
I'm experimenting range rating my boiler down and using my Nest thermostats to kind of do a hot water priority. In theory it shouldn't make much difference overall but it just means I can control the boiler not going nuts to heat a few circuits because of any distortions in the LLH.
My only theory now is with the UFH that the effect of the mixing valve at 50 degrees is somehow distorting the temperature inside the header - such that the boiler thinks it needs to keep firing even though there is sufficient hot water flowing in the UFH circuit.
I'm experimenting range rating my boiler down and using my Nest thermostats to kind of do a hot water priority. In theory it shouldn't make much difference overall but it just means I can control the boiler not going nuts to heat a few circuits because of any distortions in the LLH.
First rule of LLW design. “Thou shall not use multi tapping headers” Sorry but they are a PIN. And if systems arent perfectly matched and flow rates set correctly will leave you wide open to parasitic flow across the ports.
First thing I’d be checking is flow rate of your primary pump, Vs flow rate of your secondaries.
Something is pulling that flow water across the header rather than it circulating around it, so boiler then is ramping up as it’s running on its thermistor readings to control the gas rate. If the heat is going around the system rather than round the header it’s going to take an awfully long time before the temps are coming back to the boiler hot enough to start the modulation process
First thing I’d be checking is flow rate of your primary pump, Vs flow rate of your secondaries.
Something is pulling that flow water across the header rather than it circulating around it, so boiler then is ramping up as it’s running on its thermistor readings to control the gas rate. If the heat is going around the system rather than round the header it’s going to take an awfully long time before the temps are coming back to the boiler hot enough to start the modulation process
Guide to low loss headers - CIBSE Journal
Achieving hydraulic separation through well-designed low loss headers is key for efficient heating and cooling systems. David Palmer and Baxi Heating’s Ryan Kirkwood provide detailed design guidance, including a recommended system configuration
www.cibsejournal.com
Thanks for this. I was thinking in my novice mind that this pump flow issue could be an issue too.First rule of LLW design. “Thou shall not use multi tapping headers” Sorry but they are a PIN. And if systems arent perfectly matched and flow rates set correctly will leave you wide open to parasitic flow across the ports.
First thing I’d be checking is flow rate of your primary pump, Vs flow rate of your secondaries.
Something is pulling that flow water across the header rather than it circulating around it, so boiler then is ramping up as it’s running on its thermistor readings to control the gas rate. If the heat is going around the system rather than round the header it’s going to take an awfully long time before the temps are coming back to the boiler hot enough to start the modulation process
Guide to low loss headers - CIBSE Journal
Achieving hydraulic separation through well-designed low loss headers is key for efficient heating and cooling systems. David Palmer and Baxi Heating’s Ryan Kirkwood provide detailed design guidance, including a recommended system configurationwww.cibsejournal.com
The heating pumps are Grundfos Alpha 2s. The boiler pump is currently set to max constant pressure -
The UFH has been set to speed 1 of 3
CH to low constant pressure (I tried proportionate pressure but then it takes too long to heat the rads)
Towel rails to low constant pressure
HW to max constant pressure
I'm not sure how to check the flow rates of the pumps or circuits.
For example this weekend I noticed that for a couple of hours when just the CH circuit was calling for heat, the boiler was getting too hot and cycling. The same thing happens if only the UFH is calling for heat.
I have been trying to time the heating circuits to call for heat at the same time, which in combination with the low range rating (40% of 40kw) means the boiler only achieves a flow temperature of around 50 rather than 65/70. This lower flow temp isn't conceptually a bad thing I think (?) because the UFH mixes down to a lower flow temp anyway, and the rads can manage with 50 degrees too.
The problem is if the CH or Towel Rails also kick in, then there can be too much demand of on 16kw heat output currently from the boiler. Then the HW stays on for a really long time because it cannot heat the tanks to 50 degrees with a 50 degree flow temp.
Is there a pump from the header sending water to the underfloor pump? Technically there should be as the underfloor pump is just that. Only for circulating round the underfloor
Might the underfloor is your source of leeching.
Valves are opening up, pumps shunting water and the boiler pump is then forcing the flow across the header rather than circulate it around it as there is no separation of systems occurring
Might the underfloor is your source of leeching.
Valves are opening up, pumps shunting water and the boiler pump is then forcing the flow across the header rather than circulate it around it as there is no separation of systems occurring
Thanks - I don't quite understand what you mean - but there is a pump from the boiler to the LLH and a pump from each flow outlet on the LLH to the circuit. So one pump for UFH, one for CH, one for Towel rails and one for HW. There are no additional pumps on the UFH manifolds inside the house.
I had the UF heating only come on last night for an hour. It consumed the full power that the boiler is rated up to currently (approx 20kw) for the hour that it came on.
Can anyone help suggest what is the best back of the envelope way to calculate what the UF circuit usage should in theory be? I have an idea of the metres of pipework and pipe centres + floor area overall. Thanks!
I've also noticed that whenever the hot water cylinders come on, they also consume the full power of the boiler - even though in theory I think they should require less.
Post number of loops, length of each loop, the flow/return flow of each loop, the manifold flow/return temps or any info you have, for example if you have 9 loops with a flowrate of 2.0LPM/loop and with manifold flow/return temps of 45C/37C, dT of 8C then the UFH requires 9X2x60X8/860, = 10.04kw say 10kw and the boiler output will be exactly the same, I thought we looked at this previously?
Yes thanks we did look at this together - but what I am trying to work out is what you mentioned in your last line - if you calculate the heat demand is 10kw, this should in theory translate to the boiler needing to burn around 10kw (lets say a little more because its not 100% efficient).
But it doesn't make sense if your theoretical UF heat demand is 10kw, for the boiler to burn 20kw right? So I'm trying to work out where this heat is going and why the boiler doesn't seem to be able to modulate down to the required level. I'm not sure for example if its because of the LLH, or the impact of the amount of cold return flow from the UFH loop when it first starts up which distorts the boiler return temp.
The boiler output will always match the UFH heat demand, if the UFH heat demand is lower than the minimum boiler output then the boiler burner will cut out at the boiler flowtemp setpoint+5C and will cycle on/off to match the heat demand, simple as that, the fuel input is the boiler output/its efficiency.
Can you post a few details of the UFH as requested above?
Can you post a few details of the UFH as requested above?
Hi John, this is a schematic of what I have and which loops are typically open. I've estimated a couple of loops in orange which were added when we did an extension. Manifold 2 is one of the original ones and does not have flow meters on the heads. Manifold 1 is a new one and seems to have flow meters and I will try and do some tests today. Thanks!
Sorry I made a mistake above and am having problems editing the post. This is the schematic attached.
So as an example I just tested the family room loops for half an hour. The gas consumption according to the meter was 10.69kwh (nothing else was open). The boiler was firing at 70 on the screen and the underfloor loop flow return at the manifold was 53.8 / 43.6 (the white JG blending valve near the underfloor pump set to around 45 degrees).
The boiler is about 6 metres away from the manifold. There is no pump on the manifold and the flow meters didn't seem to move (not sure if these are flow meters?).
Gas consumption 10.69kw/30mins???, so gas consumption 21.38kwh per hour??.
What is the boiler flow temperature setpoint and what is the actual boiler flow temperature, also can you see the boiler return temperature??.
Also how many loops are open?, I am calling a loop as like one of the 8 above.
What is the boiler flow temperature setpoint and what is the actual boiler flow temperature, also can you see the boiler return temperature??.
Also how many loops are open?, I am calling a loop as like one of the 8 above.
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Yes, 10kwh! It is the zone called Family Room which I tested - so 3 loops. The boiler flow was 70 degrees, I didn't measure the actual boiler flow / return in this instance but generally from the flow tends to be measured at 5 degrees less than the boiler temp and the LLH return tends to be 10 degrees less - i.e. at 70 on screen it would be 65/55.
Still not clear if its 10.69kwh/30mins or 10.69kwh/hour.
If 10.69kwh/hour then loops emittance 10.69X85%, say 9kw, which means each loop emitting 3kw which equals a flowrate of 4.2LPM at a dT of 10.2C (53.8-43.6), I'm a bi surprised that a dT of 10.2C at that flowrate but thats what your info shows.
If the heat emitted is 18kw , 6kw/loop, then the flowrate is 8.4LPM/loop, very unlikely IMO. I normally read of loop dTs of ~ 8C with a flowrate of 2.5LPM so a loop would typically emit 1.4kw.
If 10.69kwh/hour then loops emittance 10.69X85%, say 9kw, which means each loop emitting 3kw which equals a flowrate of 4.2LPM at a dT of 10.2C (53.8-43.6), I'm a bi surprised that a dT of 10.2C at that flowrate but thats what your info shows.
If the heat emitted is 18kw , 6kw/loop, then the flowrate is 8.4LPM/loop, very unlikely IMO. I normally read of loop dTs of ~ 8C with a flowrate of 2.5LPM so a loop would typically emit 1.4kw.
It was 10kw over the half hour, so 20kw per hour.
So working on your calculation the flow rate would be 8.4 LPM. This is why I am wondering what could be taking the heat if its not going to the UFH.
I'm guessing there is some heat loss for heating up the LLH and a little bit of each closed heating circuit (the rads, towel rails and hot water) until their zone valves. Also since the two UFH manifolds are connected off one circuit, some heat would circulate to the other manifold in the house but divert through since the zone actuators are closed.
I'm not sure what else could cause the high gas usage aside from a very inefficient boiler.
It would be impossible to circulate 8.5LPM through say a 90M loop, it would require a pump with a 17.5M head, you could circulate it through 20 or 25M with a manifold pump running with a 4M head, you will circulate ~ 4LPM through 90M of 16mm (12mm ID) with that 4M head which makes some bit of sense and means ~ 10kw UFH demand but your gas usage shows twice this.
You can "prove" this 20kw usage another way, just keep reducing the boiler max output in say 2kw increments until the boiler flowtemp start falling, this will verify the consumption numbers, or not.
You can "prove" this 20kw usage another way, just keep reducing the boiler max output in say 2kw increments until the boiler flowtemp start falling, this will verify the consumption numbers, or not.
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