Low flow rates

[RogerS]

Our heating circuit consists of two pumprd circuits one for hot water and one for the main central heating. Pipe runs are long, 50m 25mm total, there and back. The main circuit works fine with adequqte flow to all radiators giving less than 10dec temp drop. The hotwater circuit although basically the same in term of pipe lengths and routing, the estimated water velocity is only about 1m in 15 sec instead of about 1 to 1.5 m per sec. There don't appear to be any airlocks, the boiler core is clear otherwise the other circuit would not work and I can only conclude that somewhere the hot watercircuit is partially blocked. So what are your suggestions? chemical cleaner or power flush. Is there any way of locating the restriction?

Many thanks

 

[EASMECH]

Our heating circuit consists of two pumprd circuits one for hot water and one for the main central heating. Pipe runs are long, 50m 25mm total, there and back. The main circuit works fine with adequqte flow to all radiators giving less than 10dec temp drop. The hotwater circuit although basically the same in term of pipe lengths and routing, the estimated water velocity is only about 1m in 15 sec instead of about 1 to 1.5 m per sec. There don't appear to be any airlocks, the boiler core is clear otherwise the other circuit would not work and I can only conclude that somewhere the hot watercircuit is partially blocked. So what are your suggestions? chemical cleaner or power flush. Is there any way of locating the restriction?

Many thanks

What system have you got now? did you change it to a combination boiler from a convetional boiler?

 

[justlead1]

Hi, Have you tried swapping the pumps over? As i could be pump failure?

 

[Cds]

I assume you have measured the flow rate by feeling when the pipe gets hot. Not perhaps the most accurate method but will give a good indication.

Does the hot water circuit behave the same when only hot water is calling? If not then it is a balancing issue in that the heating is taking all or most of the flow. If it does then there is most likely to be a blockage. Start by looking at the obvious places like the zone valve. Flushing is only likely to work if the system was working OK before.

 

[RogerS]

No, It,s an old boiler, probably Z rated!

The pumps have been renewed. The system does not have a zone valve i.e. its a fairly simple system and has been balanced as far as is possible. In fact the flow remains low in the hot water heating loop even with the other loop pump switched off, which makes me think it is a blockage.

 

[Cds]

It does sound like a blockage. Get the system powerflushed.

 

[RogerS]

Thanks it's useful to have a second opinion

 

[tony.bac]

Definitely sounds like a blockage to me. Be good to know if that is the case though, keep us posted.

 

[justlead1]

Hi. Difficult to know how handy you are? But i would be inclined to remove pump on circuit of concern, Open the pump valve on the cylinder side of the circuit and draw off water into a bucket /plastic dustbin. Note the flow rate and any air or sludge that appears, this should give you an indication of the way forward, or indeed cure the problem. Good Luck