Poor heating circulation

[jelboy]

Hi guys
I am at my wits end so could use some help please!!
I recently installed a WB 24Ri (OV boiler), honeywell 3 port and grundfos 15/50 pump onto an existing system... It was power flushed, naturally, and all seemed fine... filled it with some air issues, but I managed to clear it all and left the job happy.
The customer then called and said he has no heat downstairs (boiler is downstairs, cylinder pump and 3 port are upstairs) - I went back, bled a bit of air from the system, and by shutting down the upstairs rads managed to get it hot ds again... I balanced it up (us & ds), all rads were boiling, left and thought that was it.
He called again. No heat downstairs again. Upstairs well hot, but none down. I changed the pump to a 15/60 and eliminated the by pass as its not needed with a honeywell 3 port. I filled up again, bled air out of all the system, ran it and it took a while to clear the air but when it did the system ran great! Off I went!
Guess what? He ran this morning - no heat downstairs!!!!
I reckon that circulation is just taking the easiest route (upstairs circuit), and ignoring the downstairs... There appear to be no obstructions, cos it runs fine when it is bled and encouraged to go downstairs, pump is awesome and boiler is cool... No point going to a sealed system as the f&e is full of COLD water and its not pumping over....... SO ANY IDEAS, PLEASE???????????????

 

[echoes]

1. Anywhere in the pipework that would encourage air-locks?

2. Does having CH & HW on at the same time affect/reproduce the problem?
Are the returns teed in the correct order?

 

[dcawkwell]

Don't install open vented system therefore never have problems like this.
Convert it to a sealed system. Sorted.

 

[echoes]

My sealed system suffered from poor & reverse circulation on the downstairs rads until the return tees were corrected.

 

[Razor900]

It should still have an auto bypass its in the MIs! Not that it would make things better

Firstly balance the system properly and fit a lockshield on the return from the cylinder so you can choke it down a bit.

Must be a big house to need a 24 Ri?

 

[Agile]

I dont think that you are balancing the rads properly!

Can you explain how you do it? Or point to the instructions which you follow?

Tony

 

[swbjackson]

I had a similar problem on a sealed system. I couldn't get half of the system to work unless the lockshields on the other half were barely open. It was so critical that a fraction of a turn too far would stop the other half working. Fortunately the system was split in the airing cupboard and I fitted a balancing valve to the half of the system that was robbing the heat and throttled it down. I could then get the two halves of the system correctly balanced.

 

[simond]

It will just be a recurring airlock. Fit a few bottle airvents, or a Spirovent.

If you have ADDED the 3 port valve then have close look at the cold feed and open vent positions, as it must have worked before without balancing issues.