Lower Flow Temperature & Higher Radiator Temperature?

[berty3000]

The boiler pump head is set to "4 = constant pressure high".

 

[Johntheo5]

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?

Try and take it just before when you think the heating cycle will end.

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

Yes, take those readings as well, the boilerreturn will be a mixture of all the rad returns flow&temperaturers

 

[berty3000]

Heat Pump: How to Test and Set Your Pump Speed

We explain how to measure, work out flow rate and set your pump speed to achieve optimal performance of your boiler. Learn more now.

www.heatgeek.com

This suggests pump setting important. I think mine might be too high...

 

[nme]

Hi Berty,

How did you get on with this? My radiators are also around 5 degrees between Flow/return, and I think I’ve read the same guidance as you on this site about adjusting the lockshield valves to achieve a dT or 12 while also running at around 60 boiler temp.

Not sure where to go from here. Be interesting to hear how you resolved this in the end?

Thanks
Nathan

 

[berty3000]

Hi Berty,

How did you get on with this? My radiators are also around 5 degrees between Flow/return, and I think I’ve read the same guidance as you on this site about adjusting the lockshield valves to achieve a dT or 12 while also running at around 60 boiler temp.

Not sure where to go from here. Be interesting to hear how you resolved this in the end?

Thanks
Nathan

Hi Nathan,

So I've gone through a process of asking questions, trying things out and making observations and I'm now satisfied things are set up as well as I can expect without wasting money or time.

I've just set the flow temp to between 50 and 58 depending on how cold it is outside. The lower the better. Was 58 last week and I've now reduced to 56. It was on 52 a month or so ago. This more or less guarantees condensing and efficient use of the boiler even if the return temp is only 5 or 6 lower.

I've also made use of the TRVs. I have them set to around 3 (20C for mine), but have adjusted some to suit the situation. One was turning the rad off too soon perhaps because a bed and wardrobe is close to it and the air around it was getting warmer than the room as a whole. So that one I have slightly higher than 3 to trick it. Another one was doing opposite so I lowered it slightly. It was all a case of making repeated observations of the rads, the room temps (I have thermometers in some rooms but also used a food probe to measure air temp), and observing what the boiler was doing. Long story short, the TRVs will reduce the amount flowing through the radiator and this in itself will increase the difference between the flow and return temps, which the boiler responds to in turn as it is monitoring the situation and heating the house.

In addition to all this, I have set the pump head setting to 1 (it was originally on the highest, 4) so the speed of flow is reduced, and I have reduced the central heating output from the maximum 24KW to about 9KW. These settings have caused no problems for me.

All of this has been heating my home well, based on about three heating blocks per day (early, mid day, evening) amounting to about 7 hours. Bills have seemed reasonable.

The only other thing I could do now is also fiddle about with lockshields but I have seen no evidence that the system is unbalanced. The rads all heat up at similar pace. I haven't bothered to check the flow and return differential recently, except to say that, at the boiler, the flow is too hot to hold and the return isn't. I don't think there's a massive difference still, but given that the house seems to be getting heated fairly efficiently I don't see the point in changing anything further. I've also read online that it can be better to consider flow and return difference in terms of a %, and that a 10 or 15% difference is fine. Bearing in mind that boilers are often installed and balanced at a very high flow temperature (like 70 or 80C) this might put the 12C and 20C that gets banded around in context! My flow is always under 60C.

Hope this helps!

Ps. The other thing is that I think flow and return temps are going to vary throughout a heating cycle anyway for different reasons, so taking temps at the boiler or a radiator for a few minutes isn't necessarily going to tell you what's going on over a period of two hours. I might be wrong though!

 

[nme]

Hey,

Thanks for coming back, and glad you managed to sort your issues. I’ve been reading through those heat geek references in your last post, and some really useful information there. - Thanks for that link. Reading your experience from my non plumbing experience perspective, it seems a sensible approach. I’m currently running at 75 flow temperature but having some weather compensation controls retrofitted, just wanted to get a feel for how my current setup was performing and was thinking about looking at balancing my radiators but having read your experience and the heat geek articles, I think i’ll wait and let the new controls together with the TRV’s take care of things.
I can always review later if the new controls don’t seem to be working.

Thanks for following up, really helpful reading the conclusion.

Many Thanks
nathan

 

[Johnytuono]

Why would the mean radiator temperature stay the same if the flow temperature has been significantly increased?

Also, at what point are the benefits of increased condensing outweighed by the higher burning of gas?

I read earlier that the return temperature should be 12C lower than the input temperature at the radiators, and to adjust the lockshields if this not the case. As there only seems to be 5 or 6C difference in my radiators, is there merit in tightening the lockshields a bit? Or is this to do with something different?

If the 12c difference was when you balanced at a flow of, say, 60c, then the difference (delta) will obviously be less (5 or 6c in your case) at a lower boiler flow temperature...