Underfloor heating system not very efficient - what can i do

[BlueLoo]

You just opened my eyes here, that's 7.5hrs difference and lets say 55KW used. So does that mean that even though the boiler was on for 2hrs, it was consuming gas at the rate of approx 7.5kw/hr ? Please help me understand it.

I'm just a nerd, not a gas engineer.

However, a boiler rating is based on its max output over 1hr continuous.
Boilers just don't do that. They fire for a bit at full pelt to get the heating circuit to temp then reduce power and firing time to a level which maintains that heating circuit temp.

You've a Combi? Stick some of that into heating the water. 10kw for 300l if from cold.

Every shower ~ 4kw.

 

[Gasguru]

All modern boilers modulate...they vary their output (and hence gas consumption) to maintain the temperature setpoint.
So for example a 30kW boiler might vary between 30kW flat out down to 6kW at minimum. Once it gets to the minimum setting it will then cycle.
Some boilers have very wide turn down ratios...some Viessmanns are 20:1

For maximum efficiency short cycling is to be avoided...so system balancing is essential, all radiators should heat up evenly etc.
What's the boiler make and model?

 

[platforminc]

All modern boilers modulate...they vary their output (and hence gas consumption) to maintain the temperature setpoint.
So for example a 30kW boiler might vary between 30kW flat out down to 6kW at minimum. Once it gets to the minimum setting it will then cycle.
Some boilers have very wide turn down ratios...some Viessmanns are 20:1

For maximum efficiency short cycling is to be avoided...so system balancing is essential, all radiators should heat up evenly etc.
What's the boiler make and model?

Worcester 30kw compact ERP system boiler.

 

[flameport]

The desired room temp is 21c, what temp should i set the stat ?

21. You set it to the temperature required.
4C is the difference between that and the setback, so if you have 21, then the setback is 17.
Unless you are absolutely desperate to have 21, try 20 and 16 instead.


There are several things you haven't yet grasped the concept of:

The boiler being 'on' does not mean it's burning gas 100% of that time. The boiler will switch on/off and even when on, will adjust the amount of gas being burned to keep the water in the pipes at the required temperature.

Modern heating systems are not intended to be used by 'it's 6pm lets turn the heating on'. That was only the case decades ago when the controls were a mechanical timer and possibly a janky old analogue thermostat.
Modern systems are generally 'on' all the time, you just set the temperature required for times of the day, days of the week etc. The controls do the rest - the actual time the boiler is 'switched on' is unrelated.
In warmer weather, the boiler will be active for far less. In cold weather, a lot more. In the summer, probably not at all.

The same applies to a hot water cylinder - if 'on' 24/7, it will only heat the water when it's required, such as when someone has used hot water. Once it's up to temperature, the thermostat in the cylinder will switch the boiler off.

UFH has a very slow response time, and is totally unsuitable for turning on and off - heating up from cold is hours rather than minutes, and cooling also takes a long time, hence you don't have a massive difference between the two temperatures. 4C being typical.

 

[SpecialK]

Is the boiler stopping working due to the room thermostats all being satisfied? Then yes the UFH circ pump will most likely shut down unless it has an overrun timer.

What heating flow temp is your boiler set at? It can be set just above the blender valve temp (ideally to allow it to condense as much as possible and this is assuming you can adjust it independently to the cylinder temp)

Does the boiler cycle a lot when the UFH is on? Or does it modulate and keep going...?

What are your UFH manifold flow and return temps? The return should be sending back much colder water to the boiler.

That system water looks FILTHY!

One other observation is that when the boiler goes and stops working, the manifold pump stops also. Is this normal ?

 

[platforminc]

Is the boiler stopping working due to the room thermostats all being satisfied? Then yes the UFH circ pump will most likely shut down unless it has an overrun timer.

What heating flow temp is your boiler set at? It can be set just above the blender valve temp (ideally to allow it to condense as much as possible and this is assuming you can adjust it independently to the cylinder temp)

Does the boiler cycle a lot when the UFH is on? Or does it modulate and keep going...?

What are your UFH manifold flow and return temps? The return should be sending back much colder water to the boiler.

That system water looks FILTHY!

When the stats are satisfied then the boiler stops, I read somewhere that the UFH can cycle water down even when the boiler is not heating. Could have misunderstood this.
I set the boiler temp to eco, used to be on max before up till about a week ago. Boiler temp hovering around 55- 60 as we speak, right now I took the advice on the forum and have a longer running period 6.30am - 7pm @ 19 and after that @ 15 deg
Blending valve set to 48, just around 50deg.
Regarding your question around cycling a lot, I wouldn't know how to answer that as I don't know how to work out when its cycling or modulating, i generally don't have the boiler running for short periods.
As we speak, the system is only heating on zone, flow temp just under 50 deg, return temp around 38deg.
Regarding the flow valves, ironically when the system was last drained, filthy water didn't come out, i just don't understand why its stuck around the flow valves, part of the heating engineers job will be to sort that out and balance the system, i am here to educate myself as much as possible and inform him of all the weird things I have noticed, he would only be here for a few hours but I have observed the system for a lot longer, hence why I want to summarise it for him correctly.

Thanks in advance.

 

[Nozzle]

When the stats are satisfied then the boiler stops, I read somewhere that the UFH can cycle water down even when the boiler is not heating.

You should find there is a separate circulating pump for the UFH manifold, and another for the boiler (likely internal to the boiler unless it's "heat only". You should also find there is a separate controller for the UFH, and it gets the "GO!" signal from the timer/programmer, via the zone valve (which also fires the boiler). At the same time, the UFH controller then starts the UFH circ pump and opens the applicable loop actuators. On the closing down sequence, the UFH controller should allow the pump to over run, though it's not imperative as it's their for boiler protection. The UFH loops would be left with warm water once the zone valve is closed anyway.

You have more rooms heated now than before, so that'll largely account for the increase you are seeing.

To help your diagnosis, remember to turn off the DHW or other heating loops so your results are excluding other variables.

 

[SpecialK]

Cycling is when it turns on and off whilst the rad symbol is still lit. There will normally be an anti cycling delay of a few minutes.
When its running the UFH is the return to the boiler cold?
What is the UFH pump speed set at?
Do you know the loop lengths and has the flow been set correctly for them?

I run my UFH blender at 40 degrees as I have LVT flooring. The loops at about 2.5l/m (I think?) and the pump is on UFH setting. Most I seem to use at the moment is 5.6m3 a day but my UFH is about 25m2 and the rest of the house is on rads.

Do you have bifolds and large windows without curtains?

When the stats are satisfied then the boiler stops, I read somewhere that the UFH can cycle water down even when the boiler is not heating. Could have misunderstood this.
I set the boiler temp to eco, used to be on max before up till about a week ago. Boiler temp hovering around 55- 60 as we speak, right now I took the advice on the forum and have a longer running period 6.30am - 7pm @ 19 and after that @ 15 deg
Blending valve set to 48, just around 50deg.
Regarding your question around cycling a lot, I wouldn't know how to answer that as I don't know how to work out when its cycling or modulating, i generally don't have the boiler running for short periods.
As we speak, the system is only heating on zone, flow temp just under 50 deg, return temp around 38deg.
Regarding the flow valves, ironically when the system was last drained, filthy water didn't come out, i just don't understand why its stuck around the flow valves, part of the heating engineers job will be to sort that out and balance the system, i am here to educate myself as much as possible and inform him of all the weird things I have noticed, he would only be here for a few hours but I have observed the system for a lot longer, hence why I want to summarise it for him correctly.

Thanks in advance.

View attachment 255572

 

[platforminc]

You should find there is a separate circulating pump for the UFH manifold, and another for the boiler (likely internal to the boiler unless it's "heat only". You should also find there is a separate controller for the UFH, and it gets the "GO!" signal from the timer/programmer, via the zone valve (which also fires the boiler). At the same time, the UFH controller then starts the UFH circ pump and opens the applicable loop actuators. On the closing down sequence, the UFH controller should allow the pump to over run, though it's not imperative as it's their for boiler protection. The UFH loops would be left with warm water once the zone valve is closed anyway.

You have more rooms heated now than before, so that'll largely account for the increase you are seeing.

To help your diagnosis, remember to turn off the DHW or other heating loops so your results are excluding other variables.

Please see the picture below, I can see 2 pumps. One for the UFH which is black in colour and another which is red. The one for the UFH is fairly obvious what its for, the red one comes on all the time, but i think thats for heating and hotwater. not sure.

 

[platforminc]

Cycling is when it turns on and off whilst the rad symbol is still lit. There will normally be an anti cycling delay of a few minutes.
When its running the UFH is the return to the boiler cold?
What is the UFH pump speed set at?
Do you know the loop lengths and has the flow been set correctly for them?

I run my UFH blender at 40 degrees as I have LVT flooring. The loops at about 2.5l/m (I think?) and the pump is on UFH setting. Most I seem to use at the moment is 5.6m3 a day but my UFH is about 25m2 and the rest of the house is on rads.

Do you have bifolds and large windows without curtains?

When its running the UFH is the return to the boiler cold? ITs not cold, its hot but not as hot as the flow which is as expected.

What is the UFH pump speed set at? I have not touched this before, but please see the picture below. If i change it, it auto resets so have not really looked into it any further.

Do you know the loop lengths and has the flow been set correctly for them? This is where i am suspicious, if you notice in my previous posts, I have always talked about balancing the system. I tried to do this when a friend helped me to drain the system earlier this year, but the instructions I found on youtube on balancing the system using the flow valves didn't work for me, so i just left it for fear of not damaging anything on the system.


Do you have bifolds and large windows without curtains? yes I do , please see floor plan below, there are 2 areas the first is zone E, you will notice a 3m wide bifold door, this area is prone to high heat loss. to put it into perspective, it takes almost an hour to heat up to 0.2 degrees upwards however in the summer being south facing, it gets really hot. So what I have done is lowered the stat setting for that zone, this way 18 deg is fine. The second place is zone B, you have a door there with a glass pane just over 2m wide. Prone to heat loss also, so i decided to heat such areas as much lower temps.

Another observation, if you are using 5.6m3 a day for UFH for 25sqm thats not too bad, what temp are your stats at and roughly where are you based, the LVT definitely does help as its thinner and the heat can get to you much faster, in my case you got the tiling adhesive + thickness of tile . Lesson learnt.

 

[BlueLoo]

Do a heat loss calc.

Anything else before hand is pointless.

 

[Gasguru]

Jeez...what an absolute mess
Why the extra pump, gauge, safety valve...it's a system boiler with those parts integral.
Probably needs an additional expansion vessel.
It wouldn't surprise me if the builder did much of that work, lots of non compliance.
How does anyone get to the manifold for repairs/setting up?
Tear it out and start again for me.

 

[MeldrewsMate]

You just opened my eyes here, that's 7.5hrs difference and lets say 55KW used. So does that mean that even though the boiler was on for 2hrs, it was consuming gas at the rate of approx 7.5kw/hr ? Please help me understand it.

I think you should look again: your boiler is rated at 30kW (note the lower case k and upper case W), this means that unless you have other gas appliances of a similar power (or a large leak!) you CANNOT be consuming at a rate of 55kW.

Please understand the fundamental difference between the kilowatt (kW) and the kilowatt-hour (kWhr).
A 30kW boiler running at maximum load continuously for 3 hours will consume 90kWhr of energy from burning gas. That's equivalent to 90 'units' of electricity, and is the basis of your gas billing. Your erroneous use of the units of power and energy don't help our understanding of your problem.

UFH has a very high heat capacity, therefore it will take several hours to heat up from cold, and several more to cool down. Benefits are:
1. Warm feet and a cooler head - ie comfort at a lower room temperature; you can set the 'stats lower to achieve a comfortable environment.
2. Lower heating fluid temperatures, increasing boiler efficiency.
3. Lower running costs when set up and used correctly.
4. Capability to run with alternative (lower carbon) heating sources, such as air source heat pumps.

The downside is that it is not very responsive to changing user habits, but generally the 4C setback overnight works well for most customers.
It has been said that you have a large house, and large houses cost more to run than small houses, and therefore cause more environmental damage than smaller ones too. Your enhanced insulation will pay dividends for many years to come but, just like my old school report, '10 out of 10, could try harder' is the usual comment, meaning that there is never enough insulation!

The dirty sight glasses (and flow indicators) for the UFH can be cleaned quite easily once removed; it's the lack of access that will be the biggest headache. Once done though, flow balancing can be easily achieved by following the designer's recommendations. In their absence I suggest the following method:
1. Set the pump to its minimum speed (RTFI for how to do this), with all UFH zones calling for heat.
2. Remove every electric actuator from the manifold; make a note of which goes where, because the rest of this may take several hours to achieve.
3. Open the flow restrictor in each loop to maximum, and observe the flow rates. Restrict flow in the high flow zones to get a reasonable flow in every zone. If this can't be achieved turn the pump speed up one setting (from speed 1 to speed 2).
4. Leave the system for several hours to warm up.
5. Measure the temperatures of the pipework flowing into, and out of each zone. There should be a marked decrease in the return temperatures, but of highest importance is that each zone's return temperature should be the same within a few degrees.
6. Reduce the flow to those with higher return temperatures, again leaving several hours for stabilisation between iterations of this step.
At the end you should have one zone with its restrictor almost fully open, the pump speed at the minimum needed to circulate, and all return temperatures equal....and all rooms warmer than you would like (to pay for).
7. Replace all zone actuators, and set the room thermostats to your desired values.

Next balance the radiator system and the hot water cylinder.

Bear in mind that you have a hot water cylinder, so the boiler's target temperature should not be set below 65C (flow temperature, as displayed on the boiler) to achieve satisfactory hot water performance (55C to 60C) and legionella control. Sadly the facility of a second boiler set-point for hot water generation seems to have lost favour with boiler manufacturers.

Hope this helps.
MM

 

[MeldrewsMate]

PS: read your gas consumption each day in cubic metres, to three decimal places. You can find out from your gas bill how to convert from m3 to kWhr, and thus how your consumption varies/reduces with experience, weather conditions, and occupancy. Focussing on the cost will only introduce another variable (that you can't control), so minimise your consumption to minimise your bills...you never know, even the teenagers might get the connection between their use of heat and their environmental impact. Mention cuddly Pandas and they may even turn their lights OFF when they leave the room!!

 

[platforminc]

I think you should look again: your boiler is rated at 30kW (note the lower case k and upper case W), this means that unless you have other gas appliances of a similar power (or a large leak!) you CANNOT be consuming at a rate of 55kW.

Please understand the fundamental difference between the kilowatt (kW) and the kilowatt-hour (kWhr).
A 30kW boiler running at maximum load continuously for 3 hours will consume 90kWhr of energy from burning gas. That's equivalent to 90 'units' of electricity, and is the basis of your gas billing. Your erroneous use of the units of power and energy don't help our understanding of your problem.

UFH has a very high heat capacity, therefore it will take several hours to heat up from cold, and several more to cool down. Benefits are:
1. Warm feet and a cooler head - ie comfort at a lower room temperature; you can set the 'stats lower to achieve a comfortable environment.
2. Lower heating fluid temperatures, increasing boiler efficiency.
3. Lower running costs when set up and used correctly.
4. Capability to run with alternative (lower carbon) heating sources, such as air source heat pumps.

The downside is that it is not very responsive to changing user habits, but generally the 4C setback overnight works well for most customers.
It has been said that you have a large house, and large houses cost more to run than small houses, and therefore cause more environmental damage than smaller ones too. Your enhanced insulation will pay dividends for many years to come but, just like my old school report, '10 out of 10, could try harder' is the usual comment, meaning that there is never enough insulation!

The dirty sight glasses (and flow indicators) for the UFH can be cleaned quite easily once removed; it's the lack of access that will be the biggest headache. Once done though, flow balancing can be easily achieved by following the designer's recommendations. In their absence I suggest the following method:
1. Set the pump to its minimum speed (RTFI for how to do this), with all UFH zones calling for heat.
2. Remove every electric actuator from the manifold; make a note of which goes where, because the rest of this may take several hours to achieve.
3. Open the flow restrictor in each loop to maximum, and observe the flow rates. Restrict flow in the high flow zones to get a reasonable flow in every zone. If this can't be achieved turn the pump speed up one setting (from speed 1 to speed 2).
4. Leave the system for several hours to warm up.
5. Measure the temperatures of the pipework flowing into, and out of each zone. There should be a marked decrease in the return temperatures, but of highest importance is that each zone's return temperature should be the same within a few degrees.
6. Reduce the flow to those with higher return temperatures, again leaving several hours for stabilisation between iterations of this step.
At the end you should have one zone with its restrictor almost fully open, the pump speed at the minimum needed to circulate, and all return temperatures equal....and all rooms warmer than you would like (to pay for).
7. Replace all zone actuators, and set the room thermostats to your desired values.

Next balance the radiator system and the hot water cylinder.

Bear in mind that you have a hot water cylinder, so the boiler's target temperature should not be set below 65C (flow temperature, as displayed on the boiler) to achieve satisfactory hot water performance (55C to 60C) and legionella control. Sadly the facility of a second boiler set-point for hot water generation seems to have lost favour with boiler manufacturers.

Hope this helps.
MM

OMG !
I cant thank you enough. Your post is well written, in fact I have printed it and will be reading it every few hours. Talk of a constructive feedback, you are so good at it.
This is exactly what I was looking for, detailed, well written and very informative. It allows me to tackle the issue and I can tick things off also.
Concerning your comment around the boiler temp for the cylinder, as there are no numbers written on the boiler, i don't know the gauge for 65 deg on the knob, but i will download the manual and act accordingly.
At the end of the day, we all have our areas of specialism, heating is not mine although I always love to understand it so that when things go wrong, when others are panicking, i am at least the calmest in the house. The work was undertaken by a builder with his own contractors and very little input from me, i am just at the receiving end of the problems when the contractors are long gone.