Circulation Problems!!!

[PMH]

CH system problem – part system heats okay – one section has no return flow.

Boiler – Potterton Suprima 80L
Pump – Grundfos UPE 15-60 [set on proportional pressure
HW - Fully Pumped and always okay


CH - Flow/Return T’s off at a point where:-

Section one – 22mm pipes run down feeding top floor Lounge/Office mid floor Kitchen and part lower floor Bathroom/Bedroom and are all heat okay.

Section two – 15mm continues its run for another 5mtrs then drops down, first feeding mid floor closet, hallway lower floor two bedrooms and bathrooms the furthest point being over 33mtrs away

At the point where theT’off is the flow pipes continue to be hot as far as I can feel before they turn down but the return is cold from the T’off as far as I can feel.

I have as far as I can tell expelled the air and continued for some time allowing individual rads to get hot, but the flow is still stone cold at the T’section.

It has worked before at the furthest point but not for some time now.

My thoughts are:
- the tube is undersized or
- there is still air somewhere which effectively cuts back the power of the proportional pump speed

Would a solution be to add another pump in series and wire in parallel so that it gives section 2 more power to circulate and come on at the same time as the initial pump, if indeed it is a circulation problem.

Any ideas??

 

[ChrisR]

CLose all the rads which work, turn the pump up to full. Make sure the valves are open on the cold rads (thermostatic valve central pins, under the bit which comes off, may be stuck down)

Rads near the pump will need to be almost shut (say 1/8 turn open) to leave enough pressure for the furthest away.
"Balancing" is the word to search on.

 

[ChrisR]

As you're emailing me direct I've come back.
There's no UPE 15-60 on the grundfos website.
If it's a UPS 15-60, or an Alpha, put it on max.
You may have some sludge in the long thin pipe which will make any calculations irrelevant.
The flow you need for one rad (?you don't say what output) is tiny , but you do have to balance the system which will be hard. It takes ages to do as well. Shut all but your furthest rad. Go back towards the pump opening the rads a v small amount. Leave to stabilise and measure the temp drops across the rads- empirical and infuriating and slow.

You could try a pump on the long pipe. Make it turn on when the pipe (somewhere) is warm, so it'll stop when the heating's off - unless you can get wires through from the controls box.

 

[PMH]

Thanks for your time Chris - I managed to find the site address for the pump -

http://www.grundfos.com/web/homeuk.nsf/Webopslag/24508BE21566230180256887004D6CF5

Since my original post to you, I adjusted the pump speed to maximum. Closed all rads leaving the furthest one away open. This produced a little bit of warmth. I then tried venting but even after 5mins no air. I moved up stairs to the first rad to be supplied on section two just as it splits to drop a further 12'. Air kept coming out, but also drained off approx 10 litres of water. I went back to the furthest rad and then vented some air until no more air came out, but it was still only warm but approx 20mins later it was very hot but virtually cold on the return. I vented more air upstairs. Then bingo the rad heated up. I then found that by shutting off the return and opening it again whilst venting more air came out, this helped the return pipe to get hot. I repeated this exercise on all the rads downstairs and then opened the others one by one upstairs whilst still checking that the last was still receiving hot circulated water. As more opened so the bottom ones went luke warm.

I then went back and closed all rads leaving the furthest one open but it would not heat up, I tried venting but no air came out. I checked every 30mins and after a couple of hours with me doing nothing it went to full heat again.

Some weeks ago prior to replacing the boiler heat exchanger I pumped mains pressured water through the system as a flush, even though virtually 90% of the piping is relatively new and all the rads are less than twelve months old, just in case, it was very clean.

In total there are 17 rads approx 21Kws in total possible output.

Is it possible that air is still sitting in the pipes running under the floor downstairs and the proportional pump is not pumping at full force?

I bought an infra red digital thermometer to balance the rads, but I still cannot get the bottom rads to operate anywhere near normal so I'm at a loss.

Incidentally, the system has an old air pressure release valve and has an open vented pipe linked into the topup pipe which in turn joins way before the pump. Do you think air may still be getting in via the call for top up as I vent? Do I need an open vent as well as the APRV?

Do you think a second pump would be the answer so as to boost the supply to section two?

 

[oilman]

It looks to me you are trying to vent the system with the pump running. this can cause air to be sucked in.

Try turning each radiator on in turn, with all the others off, and open up both valves to maximum, and the pump running. If there is air in the pipes this may allow the pump to shift it.

 

[PMH]

I will try that tomorrow.

I am still wondering whether the proportional pressure control on my Grundfos UPE-15-60 pump is making life difficult whilst there is air in the system.

The manual says -

The pump differential pressure does not remain constant, but reduces as the system flow reduces. This system gives the best system control and the greatest energy saving. This mode is generally selected when the system is fitted with TRV's and requires a high differential pressure (4m or more) in order to achieve the design flow rate.

 

[ChrisR]

The air would cause flow problems in a multi-path system, as its harder to push round than water. If it ISN'T being introduced when you bleed the system then you have a serious problem somwhere. Either rampant corrosion (producing hydrogen) or air ingress through a mcro leak or bad design.

No you do not need an prv if you have an open vent. You have a feed tank at the top, yes?

The pump does seem to be making life difficult - I agree with your concerns about it reacting to the air in the system.

More than one variable makes it hard - I'd put an ordinary 15-60 in there to prove what's going on. A bit easier for me as I have a dozen or so spare...

 

[Baxi-Remeha]

try half filling a milk bottle, and putting it over the vent pipe, then get somone to turn on the pump. if the water is sucked up the vent, there is a chance this is where the air is getting in.....