Lower Flow Temperature & Higher Radiator Temperature?

[Johntheo5]

Ok, so what can I do to make the radiators release more of the heat going into them, thereby giving me more heat and reducing the return temp?

As I say, I'm only getting a 5C difference from in to out. This is whilst the boiler is burning away. When it takes a break, which it periodically does, them the in and out temperatures at radiators seem to equalise a bit. As mentioned before, all the rooms have TRVs apart from the one where the thermostat is and that radiator always seems to be the hottest.

How about the flow rate from the boiler? Could that be too high so that the water is being pushed through the radiators too quickly?

Would closing the lockshield a bit not help to keep more heat in the radiator?

Ok, so what can I do to make the radiators release more of the heat going into them, thereby giving me more heat and reducing the return?

As explained already, a rad releases a certain amount of energy based on its mean temperature and the room temperature, in the example you gave you said you had flow/returns of 49/43C with a room temperature of 20C, this is a mean temperature of 46C, you simply cant get that rad to release any more heat and maintain 20C without changing that mean rad temperature and thats it in black and white, we only showed that by increasing the flow temperature to 64C and reducing the flowrate (automatically via the TRV which senses the room temperature) to give a return temp of 28C that the room temperature will still be maintained at 20C because the mean rad temperature is exactly the same at 46C = (64+28)/2. but you get a higher condensing effect = higher boiler efficiency = lower gas consumption.

As I say, I'm only getting a 5C difference from in to out. This is whilst the boiler is burning away. When it takes a break, which it periodically does, them the in and out temperatures at radiators seem to equalise a bit. As mentioned before, all the rooms have TRVs apart from the one where the thermostat is and that radiator always seems to be the hottest.

The in/out temperatures will neary equalise depending on how long the boiler is off.
Have you checked that the TRV heads (actuators) have been attached properly, ie with the index to max, 5 or whatever the max setting is, before they are installed?.

How about the flow rate from the boiler? Could that be too high so that the water is being pushed through the radiators too quickly

The faster the flowrate the greater the output due to the smaller flow/return dT and the higher mean temperature. A TRV will just throttle down to give a reduced flowrate and mean rad temperature to maintain the desired room temperature except that the pump head is exceptionally high at say 6M as the TRVs cant overcome a dP of 6M.

Would closing the lockshield a bit not help to keep more heat in the radiator?

Why do you want to keep more heat in the rad?, closing in the L/shield to throttle the flowrate will reduce the mean rad temperature if this is what you want.

 

[Johntheo5]

... also, is there a way to get the boiler to tell me what the general flow and return temps are for the system? This will save me arsing about with a food probe at the radiators.

And does Worcester greenstar i give me the ability to check and adjust the flow rate?

Not familiar with this boiler, some boilers dont have a return sensor, but someone on here will tell you, you should then be able to see it in a menu.

 

[berty3000]

As explained already, a rad releases a certain amount of energy based on its mean temperature and the room temperature, in the example you gave you said you had flow/returns of 49/43C with a room temperature of 20C, this is a mean temperature of 46C, you simply cant get that rad to release any more heat and maintain 20C without changing that mean rad temperature and thats it in black and white, we only showed that by increasing the flow temperature to 64C and reducing the flowrate (automatically via the TRV which senses the room temperature) to give a return temp of 28C that the room temperature will still be maintained at 20C because the mean rad temperature is exactly the same at 46C = (64+28)/2. but you get a higher condensing effect = higher boiler efficiency = lower gas consumption.

The in/out temperatures will neary equalise depending on how long the boiler is off.
Have you checked that the TRV heads (actuators) have been attached properly, ie with the index to max, 5 or whatever the max setting is, before they are installed?.

The faster the flowrate the greater the output due to the smaller flow/return dT and the higher mean temperature. A TRV will just throttle down to give a reduced flowrate and mean rad temperature to maintain the desired room temperature except that the pump head is exceptionally high at say 6M as the TRVs cant overcome a dP of 6M.

Why do you want to keep more heat in the rad?, closing in the L/shield to throttle the flowrate will reduce the mean rad temperature if this is what you want.

Ok, it's making more sense now the more I'm reading your responses. Thanks for your patience and all the information.

So are you saying that a flow temperature of 64C and TRV set to 20C will be more economical than a flow temperature of 50C with same TRV setting? So higher rate of condensing trumps lower gas usage in the first place?

How do you know my radiators won't persist in their dT of ~5C and therefore result in no condensing at all from the 64C flow rate?

You seem to be saying that lockshield adjustment won't help me increase the dT. What I meant by keeping more water in the radiator is to leave more heat to radiate out from it rather than flow back to the boiler. Probably my ignorance. I keep seeing people online, including older threads on here, talking about adjusting the lockshields to increase dT. Is this because they don't have TRVs maybe? It seems to be widely understood that, during balancing for instance, adjustment of the lockshields will enable certain dTs to be achieved. Are you saying this is not the case?

Is there any merit in adjust the boiler settings in terms of its pump output, so it might be lower (reduce speed of flow througj radiators)? Or is there another way in which the pump settings might conflict with the TRVs?

I don't know about the TRVs. What's the index? They were installed by a qualified individual although radiators were subsequently removed for plastering and reinstalled by plonkers. Valves weren't really changed though, just left hanging there.

 

[berty3000]

Just one more thing, which may provide useful information. I mentioned that the system thermostat is in a room with a radiator that has no TRV. This radiator tends to be hotter than the others, presumably because the valves are fully open. I have noticed that the system periodically takes a break even though the thermostat in that room hasn't reached the 21C that I've set. Shouldn't it just keep running until it achieves what has been called for, rather than taking breaks, or is this normal?

 

[Johntheo5]

Just one more thing, which may provide useful information. I mentioned that the system thermostat is in a room with a radiator that has no TRV. This radiator tends to be hotter than the others, presumably because the valves are fully open. I have noticed that the system periodically takes a break even though the thermostat in that room hasn't reached the 21C that I've set. Shouldn't it just keep running until it achieves what has been called for, rather than taking breaks, or is this normal?

You have a combi boiler which will have a high output vs a CH boiler only so its minimum output may only be 6 to 8kw, if your heat demand falls below this then the boiler flow temperature will srise and when it reached boiler target temp+5C the burner will trip followed by a set anticycling ("break") time and will then refire, this is quite normal behaviour.

 

[Johntheo5]

Ok, it's making more sense now the more I'm reading your responses. Thanks for your patience and all the information.

So are you saying that a flow temperature of 64C and TRV set to 20C will be more economical than a flow temperature of 50C with same TRV setting? So higher rate of condensing trumps lower gas usage in the first place?

higher condensing = lower gas usage for the same heat demand.

How do you know my radiators won't persist in their dT of ~5C and therefore result in no condensing at all from the 64C flow rate?

The TRVd rads will throttle the flow to give 28C flow, the non throttled will stay more or less the same.

You seem to be saying that lockshield adjustment won't help me increase the dT. What I meant by keeping more water in the radiator is to leave more heat to radiate out from it rather than flow back to the boiler. Probably my ignorance. I keep seeing people online, including older threads on here, talking about adjusting the lockshields to increase dT. Is this because they don't have TRVs maybe? It seems to be widely understood that, during balancing for instance, adjustment of the lockshields will enable certain dTs to be achieved. Are you saying this is not the case?

Adjusting the lockshield to give a dT of 11C or whatever is primarily used to balance the system but of course you can go around and throttle them to give any dT you require but that will only give a fixed output, but if you decide to run at say a constant 64C then throttling to give say a 20C dT will give a reasonable level of condensing but only throttle the lockshield valves on the non TRV rads.

Is there any merit in adjust the boiler settings in terms of its pump output, so it might be lower (reduce speed of flow througj radiators)? Or is there another way in which the pump settings might conflict with the TRVs?

The TRVs will do all the flow control required, the pump head mustn't be too low either otherwise poor TRV control.

I don't know about the TRVs. What's the index? They were installed by a qualified individual although radiators were subsequently removed for plastering and reinstalled by plonkers. Valves weren't really changed though, just left hanging there.

The index are the numbes on the actuator that you set to give the desired room temperature, as stated above suggest starting at ~ 2.5 and only change in 0.2 increments if required.

I would also suggest that you go to each TRV, turn the actuator fully anticlockwise to max setting (5?), turn the knurled securing nut anticlockwise and remove the head, then push the pin in the valve in, it should move ~ 3 to 5mm and spring return, I use the handle of a reversed hammer to push them in/out, if operating OK, replace the actuator (max setting) and firmly, finger tighten the knurled nut, reset to index 2.5 or whatever.

 

[berty3000]

I would also suggest that you go to each TRV, turn the actuator fully anticlockwise to max setting (5?), turn the knurled securing nut anticlockwise and remove the head, then push the pin in the valve in, it should move ~ 3 to 5mm and spring return, I use the handle of a reversed hammer to push them in/out, if operating OK, replace the actuator (max setting) and firmly, finger tighten the knurled nut, reset to index 2.5 or whatever.

Will do, thanks.

For the non TRVd radiator, there is circular plastic cap on one side on a thread that turns. It pushes the pin in or out accordingly. There are no markings on it. Then there is the other valve which requires a tool to adjust (I assume the lockshield). Is there merit in adjusting the lockshield then for this radiator? Could this radiator undermine the condensing process if, at 64C, the return isn't throttled sufficiently? I'm assuming it is best for the adjustable valve to be fully open to enable the demands of the stat to be met without gas being wasted?

Might be worth pointing out that this radiator is either the furthest or second furthest from the boiler.

There is also a towel rail in bathroom. This has has adjustable knobs at the bottom on both sides by they are not marked. They do seem to open and close valves. How best to have these?

 

[Johntheo5]

Will do, thanks.

For the non TRVd radiator, there is circular plastic cap on one side on a thread that turns. It pushes the pin in or out accordingly. There are no markings on it. Then there is the other valve which requires a tool to adjust (I assume the lockshield). Is there merit in adjusting the lockshield then for this radiator? Could this radiator undermine the condensing process if, at 64C, the return isn't throttled sufficiently? I'm assuming it is best for the adjustable valve to be fully open to enable the demands of the stat to be met without gas being wasted?

The plastic cap one is actually a TRV without the actuator but very difficult to get a feel with just the plastic cap, maybe let this fully open and adjust the other side if you can, if you cant adjust this easily, just shut off the "TRV", let the rad cool down fo a hour or so, then very gradually open the plastic cap until you feel hot water entering the rad at the FLOW side, stop then and see what the return tempsettles out at, you can then adjust it i tiny amounts to give your required return temp.

Might be worth pointing out that this radiator is either the furthest or second furthest from the boiler.

There is also a towel rail in bathroom. This has has adjustable knobs at the bottom on both sides by they are not marked. They do seem to open and close valves. How best to have these?

Again, leve one fully open, shut the other fully and then reopen it maybe 1/8th turn and monitor the return temp.

 

[berty3000]

I've set boiler to 64C.

I've taken temperatures at flow and return pipes on the radiator (not the painted pipes before and after the valve, more like the pipes between the valves and radiator itself). Flow is 56C, return is 49C. TRV is set just above 3 (~21C). Room is at about 20C.

Nowhere near 28C return temperature. Just the usual 5-7C difference across the radiator.

Nothing wrong with the valve pin and TRV fitted correctly.

There must be some other variables involved. For now, I might as well just reduce the flow temperature and be guaranteed a higher rate of condensing and lower gas burn in the first place.

Question now is what can I do. Maybe balance all the radiators and adjust lockshields to achieve bigger dT (some people say lockshield adhustment is necessary even with TRVs btw), and maybe see if boiler is setup optimally.

 

[Johntheo5]

I would reduce the TRV setting to say 1.5/1.8 and see what happens, these indexes can be inaccurate but the TRV should still work well. If I set mine to 3.0 with a 20C room temp it would probably still be wide open with a low dT.

 

[berty3000]

The TRV seems accurate. Radiator started cooling off once the room was at about 20.5C. If I reduce it to 1.5 it won't come on at all. Setting 2 is equivalent to to 15C.

 

[Johntheo5]

Thats fine then, thought you said the dT wasn't changing but these TRVs are a bit sluggish, be interesting to see the final return temp.

 

[berty3000]

This TRV is set to 3.5 now (22.5C) and the radiator cools right off even though the room is only about 20C, so I'm a little sceptical about the accuracy. However, with my ones, it seems they are set too low rather than too high. They are Center ones.

 

[Johntheo5]

This TRV is set to 3.5 now (22.5C) and the radiator cools right off even though the room is only about 20C, so I'm a little sceptical about the accuracy. However, with my ones, it seems they are set too low rather than too high. They are Center ones.

Depends on where the TRV is installed, I have all mine installd horizontally on the return as I reckon it gives a far more representative romm reading also I have measured up to 3C difference at these locations, anyhow, if installed vertically at the flow end you can make allowances for this?.

 

[berty3000]

Depends on where the TRV is installed, I have all mine installd horizontally on the return as I reckon it gives a far more representative romm reading also I have measured up to 3C difference at these locations, anyhow, if installed vertically at the flow end you can make allowances for this?.

Yes, true. So basically, assume 3.5 is really 3... I've noticed this before.

I've just measured the radiator temps again. It is in a lukewarm state, measuring 42 on flow side and 29 on the other... a bit more like it. When in the heating cycle should I be taking the temperatures?

Also, is it better to just ask the boiler about the overall picture?