# flow - return differential temperature

#### old duffer

Heating season is now underway and going through tests and checks for the season
The heating return is showing a differential of 20 degrees from the flow side and some rads are just not heating at all.
(system is drained down each year)
with such a large differential, where is the heat going if some rads are not even warming up? Air?
have set the flow pressure at 1.5bar

(system is drained down each year)

Why? It seems likely to me, that there is more likelihood of a drained system rusting internally, than if it left as it is, with the water in it. Then when filled, the fresh water will include lots of oxygen, to cause more rust.

Why? It seems likely to me, that there is more likelihood of a drained system rusting internally, than if it left as it is, with the water in it. Then when filled, the fresh water will include lots of oxygen, to cause more rust.
so the energy is being lost in hydrogen production...at 58 degrees C and 1.5bar pressure....should I pattent this process?

Heating season is now underway and going through tests and checks for the season
The heating return is showing a differential of 20 degrees from the flow side and some rads are just not heating at all.
(system is drained down each year)
with such a large differential, where is the heat going if some rads are not even warming up? Air?
have set the flow pressure at 1.5bar
What is the boiler flow temperature?.

so the energy is being lost in hydrogen production...at 58 degrees C and 1.5bar pressure....should I pattent this process?

What is the boiler flow temperature?.
flow 64 degrees
return 35 degrees
Outdoor temp is reading 24 degrees (so that's wrong)
exhaust temp is 35 degrees
fan speed required and detected are the same
PWM of the fan seems low @ 39 (range is 0-1023)

That gives, effectively, a T30 rad with 51.5% of a T50 rad. which is OK at a OT temp of probably around 5/6C.

with such a large differential, where is the heat going if some rads are not even warming up? Air?
The heat is given out to air around the radiators that ARE heating up? ( guessing ). You can actually use a thermocouple or IR thermometer to measure the temp on the IN and OUT of the heated rads.

I do not think there is too much hydrogen production going on inside your rusting pipes

I do not think there is too much hydrogen production going on inside your rusting pipes
It's the rusty rads that produce hydrogen The pipes are most likely copper or plastic.

If the system is drained down every year and refilled immediately with inhibitor then maybe not a big problem but wonder why drain down every year.

If the system is drained down every year and refilled immediately with inhibitor then maybe not a big problem but wonder why drain down every year.
I remove radiators every other year (rolling yearly programe) and flush them through so as never to allow accumulation to be an issue.
It also address the pH (in that I don't have to address it) and it allows me to add citric acid which continually cleans the heat exchanger
It never allows the viscosity to increase (due to debris) and so ensures less strain on the pump
You use an inhibitor..so do I...in the form of citric acid and phosphoric acid (addressing the rust)

I have a 50 year old open vented system with combined cold feed and vent, some rads are ~ 35/40 years old and I add the odd drop of inhibitor but i know several neighbours with exactly the same set up who have never ever used inhibitor and some have equally old rads, I put it down to the fact that any (tiny ingress of ) air can escape through the open vent, I only partially drain my system every 4 years or so to renew the odd failed TRVs, also the mains water (for refilling) is of very good quality, I think, as I have a 51 year old electric Immersion.

I remove radiators every other year
Excuse my ignorance, is it not a major hassle and spills everywhere with very dirty and staining water when you try to remove a radiator?

I remove radiators every other year (rolling yearly programe) and flush them through so as never to allow accumulation to be an issue.
It also address the pH (in that I don't have to address it) and it allows me to add citric acid which continually cleans the heat exchanger
It never allows the viscosity to increase (due to debris) and so ensures less strain on the pump
You use an inhibitor..so do I...in the form of citric acid and phosphoric acid (addressing the rust)

I would suggest that is all entirely unnecessary, and probably will do more damage than it will good....

My open vented system was installed in 1985-ish. In that time, it is now on it's third heat only boiler, and second pump. The first boiler was a cast-iron battleship, which lasted 30 years, it was onl changed, along with the pump, for gas efficiency - both were running fine. I was not around, when it was replaced, but I assume the system was drained then.

The replacement, condensing heat only boiler, proved an unreliable nightmare and was recently replaced with a Vaillant, which has so far proven to be 100% reliable. I drained the system, flushed it, installed TRV's all round, and took the opportunity to swap the galv header tank, for a plastic one, and add the magnetic filter, advised by Vaillant. As said, I flushed the system, I gave it a really good flush through, end to end, top to bottom - the original water was clear, the flush water was clear, nothing at all came out of it. I have a few times checked the filter, and it have picked up almost nothing. The last time I checked it, a few weeks ago, after 12 months, and there was almost nothing in it.

I'm fairly careful about maintaining things, so this system has always had the recommended inhibitor since new. Over the years, I have never had any blockages, never had any rads not working properly, never had any noticeable debris in the system. I would therefore suggest what you are doing is at best, a waste of your time, and possibly does more damage than it will good...

Each time you drain the system, whilst it is empty, the inside of the radiators will have an abundance of oxygen, and be wet - perfect conditions to form rust. Each time you refill the system with fresh water, the fresh water will be well aerated, which is why it can take many weeks of bleeding it out after refilling, and so yet more opportunity to form rust.

Whilst I applaud the care that you give your heating system, as above I would suggest it is too much, but certainly much better than the care the average owner gives their system - judging by all the pleas for help, we see on here.

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