Radiator balance / flow rate

[dripdrip]

I have a 4 bedroom house (1986) with a Netaheat 16-22 boiler and 13 radiators.
I have replaced every radiator and radiator valves throughout, only the bedrooms have TRV's.
I replaced the pump with an Alpha 2 15/60, plus new Room Stat and new Cylinder Stat.
While changing the rads I opened each rad valve one at a time to check flow rate, all seamed good.
When I balanced the radiators I have had to close the LS valves so much (between 1/8 to 1/4 turn) to get all rads warm that the return on all rads is stone cold as is the bottom of the rads.
If I turn off any 2 or 3 rads I can improve the situation but not with them all on.
As I am not a plumber I am now stuck for ideas and would be grateful for any advice.

Thanks

 

[jefaz]

Maybe an airlock in the system somewhere?
Try turning all bar one off as this can sometimes push air if there is any
Do this for every rad,u will know if there is air as you will hear it!
Sludge in your system? I know you have changed all rads so that shouldn't be much of a problem!?

 

[dripdrip]

Thanks Jefaz, I will give it go

 

[Hardy1]

turn of the rads from there valves that are working, sleave the 3 rads on which arent working, set pump to full, and should blast the airlock out, if not then then turn them off seperately and do it individually, if not get a central heating engineer out.

 

[diamondgas]

dripdrip ... what size radiator supply pipes have you got? It sounds like you have a flow issue to be honest. Is the pump running quiet or can you hear air rushing through it?

 

[AWheating]

if you increased the size of the rads then you may find the pipework is now undersized?

 

[dripdrip]

Hi diamondgas,
I have 28mm from the boiler to the pump, 22mm from the 3-way valve and 15mm to the rads.
I have the pump set to CP2 (max constant pressure) and I can hear air passing through the pump, this also causes a bit of kettling in the boiler.
As yet I have not got this air our dispite bleading all the rads and the HW coil.

Thanks for your help with this

 

[diamondgas]

dripdrip ... Pipes sound like they're decent size. It may be that the air is just circulating around the hot water circuit. Try turning your programmer to heating only or turn the cylinder stat off! That way you'll push any air into the radiators where it can be bled off ... Also may need to turn off any manual bypass valve if there's one fitted.

Still sounds like you have a blockage of some sort either airlock or something more physical! ...

 

[brianc1]

dripdrip. if you have an open vented system and you have now put in a stronger pump it is possible that you are sucking air in through the open vent(depending on pipe configuration). like the lads say you seem to have a flow problem which can be cause by several things. your pipesizing sounds ok , so i would do like the lads say and open one circuit at a time and try force the air somewhere it can be vented. if you are happy all the air is out you may have a blockage or a pump problem. i havent fitted many alphas and cant remember if they can be vented, maybe one of the lads could tell you this.

 

[dripdrip]

Hi all,
I have tried your suggestions over the weekend.
I turned off the HW, closed off all the rad valves bar one and set the pump to max.
I ran the heating through that one rad for 10 mins then closed off the rad and moved on to the next one.
I did this for all 13 rads in the house, finally I bleed all the rads.
During this process each rad got red hot as expected.
Sadly on completion there is little or no improvement on the original problem, I still cannot get all radiators properly hot and there is still kettling in the boiler.
I can only assume that the flow is inadequate due to debris in the pipes.
As the Pump (Alpha2L 15-60), rads and rad valves are all new would I be advised to get the system powerflushed ?
Any other advices appreciated. Thanks a lot.

 

[brianc1]

dripdrip, you never said why u changed all the rads... did you have problems with them originally? were there cold spots on the bottom of the rads, if so this is a sign of sludge build up. the one thing that confuses me about alpha pumps (i have asked a few plumbers and they couldnt explain it) is how exactly they work. i am told that as rads close down there is an increase in pressure loss and the pump reacts by slowing down accordingly as it doesnt need as much flow rate/volume. i always wondered if you have a sludged up system would dirt in the system not block up on fittings or valves hence simulate valves closing and then slow down the pump at a time when you need more performance from your pump?? any toughts on this?????

 

[brianc1]

also dripdrip, you probably cant tell where your 22mm pipe reduces to 15mm, is it possible you have 5 or 6 rads being fed by 15mm?

 

[dripdrip]

Hi brianc1, Your understanding of the Alpha 2L pump is the same as mine, due to this I am only using it on CP2 (max constant Pressure or on the traditional number 3 setting, both of which are constant and do not adjust pusp speed based on demand)
There are the standard 1, 2 & 3 pump speeds as well as Proportional 1 & 2 and Constant 1 & 2.

I changed the rads because the original ones had been badly painted over the years and where rusty in places, it was easier to put new ones in.

Sadly I don't know where the 22mm changes to 15mm so it could be anywhere.

Thanks for taking the time to help.

 

[diamondgas]

I don't know if I've mentioned this B4 dripdriip but the way to find out if you have circulation issues is to check the difference in temp between the Flow and Return at the boiler! 11 - 20 DegC ... Higher differential readings gives you an indication of the size of the restricted flow

 

[fuzzy]

I have a 4 bedroom house (1986) with a Netaheat 16-22 boiler and 13 radiators.
I have replaced every radiator and radiator valves throughout, only the bedrooms have TRV's.
I replaced the pump with an Alpha 2 15/60, plus new Room Stat and new Cylinder Stat.
While changing the rads I opened each rad valve one at a time to check flow rate, all seamed good.
When I balanced the radiators I have had to close the LS valves so much (between 1/8 to 1/4 turn) to get all rads warm that the return on all rads is stone cold as is the bottom of the rads.
If I turn off any 2 or 3 rads I can improve the situation but not with them all on.
As I am not a plumber I am now stuck for ideas and would be grateful for any advice.

Thanks

have you increased any rad sizes? checged them for doubles, convectors, added any rads?
check size of pipes to em