Air in CH system and hot water returning to FE tank via the cold feed

[Tiggy1955]

I have a problem with air being sucked into my CH system creating airlocks in the radiators. The water is flowing back into the FE tank via the cold feed pipe. I can feel warm water coming through the feed pipe back into the tank as the tank water level slowly get higher. I can hear the overflow gurgling in the FE tank.

The system is 20 years old but the Worcester Bosch boiler is only 9 years old. All has worked perfectly well. I did have the classic blockage where the cold feed meets the hot return but the clogged pipes have been cut out and replaced.

I have fitted a new pump and it is set to the lowest speed. All of the radiators have been bled many times and balanced.

So the heating is working fine except that I have this problem of the air displacing the water back to the FE tank. The water it getting back into the tank a quite a rate - I would say about 2 litres per hour. This means that the rads need to be bled constantly.

Any ideas? Could it be an problem with the boiler itself?

 

[Ric2013]

Have you tried asking Grundfos? I think that's where I got the file for the VERY old Selectric pumps from. Rang them and asked for the curves IIRC.

 

[doitmyself]

Can you post any links (charts etc) to a UPS 25-50 Selectric, power outputs 40W, 65W & 95W. (installed in a new build house in 2005/2006), still running.
Thanks.

The curves are exactly the same as for the UPS 15-50 Selectric of the same vintage. The innards are the same, it's just the connections which are different.

 

[John.g]

The curves are exactly the same as for the UPS 15-50 Selectric of the same vintage. The innards are the same, it's just the connections which are different.

ref post#61
File "selectric UPS pumps old" shows the UPS 15-50 with power inputs of 35/45/50 watts. In "selectric very old" it shows the UPS 15-50 with power inputs of 40/65/100 watts with different speeds/curves, my query pump, a UPS 25-50 has power inputs of 40/65/95 so I will assume that the pump curves are similar to the latter one, above, its a 2005/2006 install. I wonder what was the time span period for the UPS 15-50 35/45/50 watts.

 

[doitmyself]

Here is the info you are looking for. The PC 9706 on pump data plate (see pic of the pump) shows that it was in production in 1997.

 

[John.g]

Here is the info you are looking for. The PC 9706 on pump data plate (see pic of the pump) shows that it was in production in 1997.

Thanks for that data.

 

[John.g]

Here is the info you are looking for. The PC 9706 on pump data plate (see pic of the pump) shows that it was in production in 1997.

Just received a photo of the pump, it seems a difficult one to track down, I presume the PC 0414 means it was manufactured in 2004.
Thanks again

 

[doitmyself]

I presume the PC 0414 means it was manufactured in 2004.

Week 14 of 2004 to be precise.

It's instructive to see how the performance of the 'same' pump has changed over time. (You should have three versions now.)

 

[Ajlsat]

sure i am in wrong place, can someone direct me. where to ask question ref heat pump instalation.thanks

QUOTE="John.g, post: 1022186, member: 99812"]I suppose we should bear in mind that the UPS2 hasn't true fixed speed curves. Even speed 1 will give a constant head of 4M from 0 to ~ 6 LPM before the head starts falling, (any real fixed speed pump head starts dropping immediately on flow demand) which with modern zoning/TRV's etc will cater for over 6 kw of heat demand at a deltaT of 15C. and with the retro fitting of condensing oil/gas boilers the trend is to get a greater deltaT of 20C to enhance the condensing effect thus leading to even lower circulation rates. So in a house with even just basic insulation could very easily be running the UPS2 pump at the ridiculously high head of 4M on "fixed speed" for significant periods of time.
I havn't any pump curves for the older UPS pumps but I would think that they would have been operating at least 1/1.5M lower head?
Having said that the 3M PP head is a bit mean to say the least and certainly will fall short in a lot of instances as on PP control the head falls with reduced flow demand so to cater for both full heating flow rates and reduced demand it would have been nice if 3.5M to 4M was available, as was pointed out above, The UPS 3 has now got a 3.6M PP head. (AND has two CP (constant pressure) settings as well!)
This one may have been replaced in a lot of cases by the UPS 2.
https://product-selection.grundfos....tid=GMA&productnumber=97549426&qcid=501056454[/QUOTE]

 

[SJB060685]

So if your ballcock were not refilling the F&E, and no overflowing took place, you think the volume of water in the system would stay the same? There isn't any being added, by, say, a leak from the coil in your hot water cylinder?

Took the words out of my mouth lol

 

[John.g]

Took the words out of my mouth lol

The air in the rads is/was displacing the water??

 

[SJB060685]

The air in the rads is/was displacing the water??

Well any air in the system will displace water. I thought my post was agreeing with someone suggest a split in cylinder coil?

 

[John.g]

Well any air in the system will displace water. I thought my post was agreeing with someone suggest a split in cylinder coil?

I thought the OP ruled that out by changing the pump settings to PP control which reduced the pump head and stopped the water returning to the feed & expansion tank and drawing air in through the vent. If the coil is split he would be getting a continuous overflow from the F & E Tank.

 

[SJB060685]

I thought the OP ruled that out by changing the pump settings to PP control which reduced the pump head and stopped the water returning to the feed & expansion tank and drawing air in through the vent. If the coil is split he would be getting a continuous overflow from the F & E Tank.

Yeah but I thought I said that before I’d read every comment lol. I know you suggesting or whoever it was to make this adjustment solved it.