Measuring Flow In Central Heating Pipes

Check out ultrasonic flow meters.

The fact that it's inconsistant does sound like air in the system.

If you turn off the valve upstream of a radiator until it gets cold, can you then turn it back on and see how long it takes to get hot on the exit pipe?

Just a thought...

Yeah, it can be a nightmare.

I ended up having a separate circuit for upstairs and downstairs, all the main pipework running under the upstairs floor....

Of course I then couldn't get air out or the downstairs section as it was one big inverted U... ended up with plumbing the bathroom towel rail into the downstairs circuit so I could bleed the bleedin' thing.

I feel your pain. I don't think thermostatic rad valves are actually a very good concept... they are seldom in a suitable airflow, and as they open and close it effects the rest of the system... I only have a few, mostly upstairs, so that as they open just a fraction you can heat the water whistling through.

Can I suggest pump speeds as another variable to play with (just in case you haven't enough)

Del

This is definitely out of my league, but I thought something like these flow balancing devices was used in these systems.

Hi Evan, I'm a rank amateur but wrestled for decades with hydronic systems when I lived in the UK.

In a sense, you don't really need a flow meter 'cos if it isn't getting hot, there isn't any flow! One of 3 possibilities spring to mind: 1. The pipework or radiator in question is blocked, 2. There is a build-up of gas in that circuit or 3. The other legs of the circuit are hogging the flow.

What I used to do is close the stop valves on all radiators except the dubious one and start the circulating pump. You will surely hear a rushing sound in that one radiator if there is flow and gurgling if there is gas in it. Stop the pump and bleed that radiator. Repeat if needed. If there is no evidence of flow you must have a blockage.

When you are happy there is flow, leave the stop valve fully open on that radiator, start the pump again and with the boiler on a low temp setting just crack open the stop valves of the other radiators. Any thermostatic valves should be set to max temp during this operation. As the radiator temperatures settle down, open the stop valves slightly on the cooler ones to manually balance the system. Finally, set the thermostatic valves again, et violà!

Glad I live in the tropics, now. Good luck.

Search clamp on ultrasonic flow meters on the Web. The first hit shows a battery operated unit that is precisely what you want. Then search your local instrumentation hire companies. This type of equipment is likely to be available on hire for a few days at a much lower cost than purchasing.

Is this a pressurised system or an unpressurised system with a header tank? If a header tank, is it filling correctly?

Usually one lets all the air out of any rads, automatic valves are best, each radiator upstairs should have one...they are quite cheap. Some long runs of pipe may need to be separately cleared of air.

The may not be any areas of pipe that rise and fall again, air will collect at the high point it only needs to be half the width of the pipe to be a problem. Check with a level.....a quick fix would be to add an automatic air valve at the high point.....but not pretty....

Make sure you know which side is the hot supply side. I have even seen pumps put in backwards, pumping the wrong way!!!

On each radiator, you should have a thermostat.

This must be the hot supply side. Check MOST carefully! Do not make ANY guesses. Having one wrong will always cause problems....

Make sure that there are no hidden isolation valves anywhere. If yes, open fully. I can isolate my heating in several places as well as being able to remove any rad while the heating is working without losing water, other than that in the rad of course!

On the other end of each rad (the cold end!), you should have an adjusting valve, often it can only be turned with a special tool, it may have even a removable cap.....if you don't have these, all bets are off!!! Give up!!

You open all of these "adjustment" valves fully.

You then open all the thermostats fully.

You switch the heating on hot.

You feel which radiator(s) get hot.

You close this/these valve(s) completely and open them say half a turn.

Make a cup of tea.

Drink it.

Make sure that the rads that were hot are still hot, if not open up another half turn on those that have cooled only.

Go and see if any other rads are now warming up.

Close the adjustment valves on these rads and open one turn. One and a half turns may be needed...

Make a cup of tea.

Drink it.

Check that all rads you have adjusted up to now are staying hot.

See if any other rads are now heating up.

carry on until all are hot all at the same time.

Replace caps on all adjustment valves.....

Go and drink a beer or two.

Relax and stay warm!!

The principle is that a rad close to the heating system has a low resistance and the hot water passes through easily. Which is why these rads need to have the flow reduced.....

Till basically every rad poses the same sort of resistance to water flow.....

It is possible that your pump is damaged or running slow or something. Or the system is silted up and needs blowing through, or somewhere a kink is in a pipe somewhere....

I have balanced both pressurised and non pressurised using the above method with 100% success...

It works with underfloor heating as well!!