Condensing combi boiler high flow

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My problem is that there is too much flow. I can easily get the furthest radiator to 70'C by restricting the other one. my problem is to have them all have a 20C temperature drop across.

Lack of flow, if you have isolated other rads, will be due to blockage or pipe side/ distribution.

With all the rads on, let the system stabilise. If it takes time, so be it. Obviously the closest radiator will be favoured by the pump. Close the lockshield on that radiator and then open a quarter turn for starters. Take it from there

Also check the temperature of flow and return at the boiler. Return water will be the average of all the returning water temperatures
 
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flow was high due to cold weather and it didn't meant to achieve 20'C drop?

Why not?
What thoughts do you have to assume such a thing.
The radiator is there to replace heat lost from the room
When temperature outside is say at 15 degrees and your room design temperature is 20, your radiator only needs to make good the 5 degrees.
Now let the outside be -1. Now the room loss is far greater. Make good is by means of boiler going at full tilt. Cannot see how the radiator differential is suddenly going to be all that different from summer season.
 
If you put a zone stat in a hall, it needs to have a rad in that space. Otherwise, the stat will remain in a cold condition and heating will be on continually in the bedrooms, be that limited by trvs if fitted, and if so, putting the boiler in a state of constant bypass as it spends most of its time just heating up the zone circuit.

The alternative solution I can think of for this is to down size the radiator in that room or move the thermostat to other side of the same room. I have another solution explained below to eliminate both thermostats and use digital TRVs. It’s going to be long but might give someone in my situation some foot for thought in future. Please skip to the end to see what I did.

I did some study and I think if found the problem and system is working fine. The installation manual seems to be inheriting many things from older boilers which are not relevant.

This boiler has an automatic pump that keeps the “flow” constant. All information available online and the installation manual talk about a specific temperature drop over radiators. This is only applied to systems with constant head pumps. I.e. those that you set the speed. if we use an analogy to electric circuit, to have constant flow (current) on each radiator, you have to adjust the pressure drop (resistance) when we have constant supply pressure(voltage). Since the heat is proportional to amount of hot water that passes per time unit (flow) we can use temperature drop to measure it relative to other rads.

The pump in my boiler maintains a constant flow (current) automatically. That’s why even if I almost shut all valves, it will ramp up the speed and pressure to maintain the flow. Therefore regardless of valve position, the same amount of flow passes and temperature drop would be the same. Of course this until pump reaches its max limit that is not logical to run it at that all the time.

How the flow is decided? My boiler has a weather competition outdoor sensor that is simple 10k NTC. It also has a “room temperature knob” that according to manual it should set the desired room temperature. It doesn’t explains but what it means is that you could scrap the room thermostat and let the system control everything. It will use delta T between flow and return at boiler to figure out actual room temp instead of a wall sensor and it uses outdoor sensor to predict room temp easier. Think of it as a built-in opentherm thermostat. Then you could use TRV for each individual room. You probably have to over design the system to achieve it.

Unless you use digital TRV with timer, you cannot switch off like downstairs automatically over night. Also they should be wifi enabled otherwise for each change you have to adjust all of them every time. (This is another solution for me)

for my situation, there are two zones. two room thermostats eliminate the benefit of having a system that quickly can adjust its output. Therefore it runs at a constant output and shuts down the system until room is colder than desired. Let’s use another analogy and use cruise control as an example. It’s like you want to travel at 50mph but set the CC at 70mph. Then manually (like my thermostats) cancel the CC when you reach 52mph and resume when speed drops to 48mph and go on. The problem with that is, ECU thinks you want to reach 70 when you resume so car wants to accelerate harder. While when you set the cruise at 50mph, it reduces the throttle before 50mph and keep the throttle adjusted using engine load instead of speedo changes. It runs way more efficient. Unfortunately this is my current setup and it has to change in future.

another alternative solution is to use a multi zone opentherm room thermostat that does the same thing but because I have two, I can stick to mechanical TRVs.

My boiler uses outside temperature and set point at knob to decide about the flow. It also sets the output and return temps to define system output. When I first attempted the balancing, outside was around 3’C and I had knob at 25’C. Using the graph below, it was running at around 70% of its max flow. I thought if I have system balance at highest flow (70%), it will not cope with lower flow rates. I decided to balance it at 30%. I had two ways, drop the knob to 11’C that at 5’c outside will have pump running at 32%. It worked but the burner didn’t kick in because return was 20’C. I found that at 20’C outside, sensor resistance should be 12.5kohm. Replaced the sensor with a 12.5kohm resistor and set the knob to 22’C. Even with low flow, I didn’t need a 20’C drop as explained above, instead , I adjusted the lockshield valves to have the same flow temperature at the inlet of each radiator. This was normally around 2-3’C below boiler output. Interestingly, at the very same position the noise at lockshields were eliminated. Reconnected the outdoor sensor. Set the knob to near max. Had the system run for couple of hours and I noticed the boiler is doing its job. Sometimes on the same radiator delta T was about 20’C and sometimes 2’C. Also the burner is not on all the time when pump is working. I guess unlike normal condensing boiler, a combi would benefit from the exhaust gases at any temperature due to very high flow, high efficiency heat exchangers and because of its control on burner output power, it doesn’t need 20’C, it will drop gas flow until there is enough exhaust heat to be absorbed by return water. I check the flue gasses regularly and there is no fog coming out anymore.

now rooms heat up more uniformly and it can reach temperatures I want. In the past, even if I set room thermostat at 27’C, so long as the knob was set to 22’C it would never reach 27. Because system automatically reduce the output power to minimum when return temp suggests room is at 22’C. Room stat is nothing more than a timer when the knob is not set at max.
 

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Then why is a boiler interlock mandatory on all boilers
I guess a smaller portion of installations are using this type of boiler and it is more of a belt and braces. If anything goes wrong with the system, it prevents running the boiler all the time. I meant room thermostat is not necessary to control room temperature in this type of boiler.
 
On the contrary thus boiler is a bread and butter go to on many estates new and old


I guess a smaller portion of installations are using this type of boiler and it is more of a belt and braces. If anything goes wrong with the system, it prevents running the boiler all the time. I meant room thermostat is not necessary to control room temperature in this type of boiler.

Can you expand on that? How else, without a TRV, are you going to control the room temperature. I am not talking about active TRVs as this item does not suit or is affordable for a lot. A lot of end users cannot even work a standard programmer.
 
I have recently changed a radiator in toilet downstairs with a column type and it didn’t warm up properly.

Column types are not as efficient at outputting heat as normal radiators, but it none the less ought to get warm/hot. Some column radiators have to be installed with the flow and return pipes connected to a vertical radiator correct ends, because they include a baffle. The baffle will restrict the flow, if the flow and return go to the wrong ends. Some of these can have the baffle moved to the other end. Did you check this point before installation?

If these pipes are wrong and the baffle cannot be changed, you might be able to turn the radiator completely round, front to back. Failing either option, the only way is to re-pipe to correct it, so pipes cross over.
 
On the contrary thus boiler is a bread and butter go to on many estates new and old
On older states, they have larger diameter copper pipes and different type of rads perhaps storage tank, etc. In new estates they have small diameter pvc pipes and houses are generally smaller and are better insulated.

Can you expand on that? How else, without a TRV, are you going to control the room temperature. I am not talking about active TRVs as this item does not suit or is affordable for a lot. A lot of end users cannot even work a standard programmer.

for individual rooms you use a TRV but the temperature in warmest room can be set by this type of boiler. You set the nominal temperature at the boiler and that sets the flow rate using the difference between nominal temp set point and outdoor temp. It adjusts the pump speed to compensate for outdoor temperature.
Indoor and outdoor delta is proportional to heat-loss. Flow rate is proportional to the central heating output. Once you have them equal room temp is maintained. Under this steady state condition, return temp defines the room temp. It’s not the exact figure but because everything is proportional you can adjust it later. Like you set it to 22 and get to 19. Then set it to 25 and you get 22. For each individual room TRV will control the temp but it has to be below 22 in this example.
 
Column types are not as efficient at outputting heat as normal radiators, but it none the less ought to get warm/hot. Some column radiators have to be installed with the flow and return pipes connected to a vertical radiator correct ends, because they include a baffle. The baffle will restrict the flow, if the flow and return go to the wrong ends. Some of these can have the baffle moved to the other end. Did you check this point before installation?

If these pipes are wrong and the baffle cannot be changed, you might be able to turn the radiator completely round, front to back. Failing either option, the only way is to re-pipe to correct it, so pipes cross over.
Yes I check the heat output rating of the column radiator against the existing one and they were identical. The radiator had flow and return inlets marked and followed that. My has PVC pipes with push fit fittings and it’s very easy to switch them. The radiator is warm as normal now after balancing the way mentioned in previous posts.
 
On older states, they have larger diameter copper pipes and different type of rads perhaps storage tank, etc. In new estates they have small diameter pvc pipes and houses are generally smaller and are better insulated.

I can assure you, you are misinformed in what you say. I have been a heating engineer for 30 years and can assure you there are large estates with new build that use I deal boilers and none of these hoses have CWS cistern


for individual rooms you use a TRV but the temperature in warmest room can be set by this type of boiler. You set the nominal temperature at the boiler and that sets the flow rate using the difference between nominal temp set point and outdoor temp. It adjusts the pump speed to compensate for outdoor temperature.
Indoor and outdoor delta is proportional to heat-loss. Flow rate is proportional to the central heating output. Once you have them equal room temp is maintained. Under this steady state condition, return temp defines the room temp. It’s not the exact figure but because everything is proportional you can adjust it later. Like you set it to 22 and get to 19. Then set it to 25 and you get 22. For each individual room TRV will control the temp but it has to be below 22 in this example.

How do you explain this to BC. How do you bypass filling in the Benchmark logbook that asks for boiler interlock
 
I can assure you, you are misinformed in what you say. I have been a heating engineer for 30 years and can assure you there are large estates with new build that use I deal boilers and none of these hoses have CWS cistern




How do you explain this to BC. How do you bypass filling in the Benchmark logbook that asks for boiler interlock
I appreciate your expertise and that’s why I am here. I have no idea about the regulations. What I explained is based on readings I have done recently, some tests that I will share once it’s done and a bit of my engineering background.

for this particular one, I got it from following document. Quote:

The On and Off time control of central heating should be controlled by a separate timer.
During programmed On times the Central Heating Radiator Flow Temperature is controlled by the boiler relative to the Outside Temperature as shown in the diagram.
The Room temperature can be adjusted using the Central Heating Temperature Control Knob on the boiler as follows. Essentially rotating the knob clockwise increases the room temperature and rotating the knob anti-clockwise decreases the room temperature.
The Room Temperature Setpoint in the associated graph is not directly related to the Actual Room Temperature but is the Nominal Room Temperature during a programmed CH period.

This can be adjusted between 5 and 30 degrees by the CH Potentiometer Knob on the Boiler when the Outside Temperature Sensor is connected. The graph only shows temperatures between 12 and 30 degrees for clarity.
Example:
1. If the CH Potentiometer Knob is set to display 22oC on the Boiler Display the Room Temperature Setpoint will be 22oC and the curve 22 will be followed, indicated by 11th curve in from the left hand side.
So as the outside temperature varies the Flow Setpoint to the CH circuit will increase and decrease proportionally.
2. If the CH Potentiometer Knob is rotated fully clockwise, the Boiler Display will read 30oC and the Room Temperature Setpoint will be 30oC hence the curve 30 will be followed.
3. If the CH Potentiometer Knob is rotated fully anticlockwise, the Boiler Display will read 5oC and the Room Temperature Setpoint will be 5oC. This is an unrealistic Room Temperature Setpoint for a CH period during an ON time, but it is calculated internally for managing Frost Protection for the system based upon Outside Temperature.”

https://idealheating.com/uploads/documents/user-guide-outdoor-sensor.pdf
 
Page 4 of that document. R/S at terminal 4&5 page 4 is a room thermostat :whistle:
It is part of the circuit
Programmer or timer cannot run the boiler unless appropriate thermostat is calling.
 
Page 4 of that document. R/S at terminal 4&5 page 4 is a room thermostat :whistle:
It is part of the circuit
Programmer or timer cannot run the boiler unless appropriate thermostat is calling.
Even there they call it timer. I am trying to check the difference. I set then thermostat to 27 when I need heat and 10 when I don’t. The rest is done at the knob. Want to see the difference to when I set the knob to max and set the thermostat at 22.

So far I have seen an advantage. When knob is at max and both zones reach the set point, both zone valves close and pump run for 2-3mins to dissipate the 60-70C water in the circuit. But water can only go as far as ABV and returns. The water in the boiler is about 60 when pump is off. While when I leave zone valve on and set knob to min, it took about 45mins!! For the water to reach about 30C! All that heat will be taken away from exhaust when I use thermostat.

page 4 to 6 refer to ideal models “Heat, Logic System and Vogue”. Apparently only them need specific wiring. Mine is “Logic+ Combi ESP1 35”.
 
page 4 to 6 refer to ideal models “Heat, Logic System and Vogue”. Apparently only them need specific wiring. Mine is “Logic+ Combi ESP1 35”.

Take it from me, Your boiler must ALSO be fitted with a thermostat
https://www.freeboilermanuals.com/assets/pdf/ideal/204978.pdf
Page 66
Section for Controls, boiler interlock. It is a requirement. No options

JohnD, a heating engineers needs to go through hoops and loops to be compliant. A DIYer can do what he or she likes.
 

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