Balancing rads help.....

[Dee]

Hi

I have 2 rads that will not heat when other 27 rads are running.

I've turned all other rads off both flow and return and the 2 cold rads are now hot. What does this tell me?

What do I do now please? 

[SteamyTea]

To me it says that the two radiators that stop working have a higher pipework resistance to them, or from them.

Like electricity, water will take the path of least resistance.

So it is probably a case of balancing (maybe a greater flow rate will help), but if there are TVRs fitted, then that complicates it all.

[Dee]

I've got those 2 working by turning off all 17 other rads at both f and R and forcing the heat to them....worked! then going back through each rad, turning back on and tweaking the return side. 

I stopped last night with 4 furthest from the boiler to balance....this morning I can't get those 4 to heat up!!

They're all column rads with TRVs

 

[Dee]

So....if I go back along the chain of rads that preceed the 4 cold ones, do I tweak the lockshields more closed or  more open?

[JohnMo]

35 minutes ago, Dee said:

So....if I go back along the chain of rads that preceed the 4 cold ones, do I tweak the lockshields more closed or  more open?

You are trying to make the system resistance similar everywhere. So if some parts are not getting enough flow, you have to increase resistance elsewhere, by closing the LS a little.

[Dee]

Thankyou for clarifying that!

Other issue is I'm not achieving anything close to 12⁰ across any of the rads try as I might....at the boiler the difference is only 9⁰

[JohnMo]

1 hour ago, Dee said:

Other issue is I'm not achieving anything close to 12⁰ across any of the rads try as I might....at the boiler the difference is only 9⁰

Are you room warm enough is your boiler running without too much cycling?

 

dT is all to do with flow rate, if you moving too much water through the system dT will be low. You could turn down your circulation pump. But if circulation pump speed is controlled by boiler then the boiler is happy with the dT so don't mess with it.

[marshian]

1 hour ago, Dee said:

Thankyou for clarifying that!

Other issue is I'm not achieving anything close to 12⁰ across any of the rads try as I might....at the boiler the difference is only 9⁰

Why is 12 deg important to you?

 

At 70 deg flow temp you might see that at the boiler but not if you are running flow temps the allow the boiler to be in condensing mode all the time

 

27 rads is a lot of rads do you have control of the pump or is it inside the boiler - if external I’d try a faster pump speed - it could be that there just isn’t enough pump pressure to overcome the circuit resistance at the extreme ends of the system

 

[marshian]

22 minutes ago, JohnMo said:

dT is all to do with flow rate, if you moving too much water through the system dT will be low. You could turn down your circulation pump. But if circulation pump speed is controlled by boiler then the boiler is happy with the dT so don't mess with it.

dT is also related to flow temp - lower the flow temps the narrower the dT will be (for same circumstances)

[Dee]

That's always quoted as being the ideal temperature across f and R...I don't know enough to question that;)

 

At 70 deg flow temp....Boiler is set to 60⁰

 

27 rads TYPO! There are 19rads

Edited 5 hours ago by Nickfromwales
Thread tidied

[JohnMo]

1 hour ago, Dee said:

What is cycling??

Every time the boiler starts and stops. Short cycle time affects gas consumption in a bad way. So an on/running time of about 6 mins or less isn't good.

 

1 hour ago, Dee said:

it's set to 3.

If I turn it down will that effect the power to push the water to the end of the house

Cannot answer that, you would have to try and see what happens.

[marshian]

@Dee please learn how to quote properly - write your responses under the quote of the post you are replying to - it’s horrible to untangle a mangled response where you’ve replied inside the quoted post

 

 

(Thread now tidied  )

Edited 5 hours ago by Nickfromwales
Housekeeping

[marshian]

3 hours ago, Dee said:

That's always quoted as being the ideal temperature across f and R...I don't know enough to question that;)

 

At 70 deg flow temp....Boiler is set to 60⁰

 

27 rads TYPO! There are 19rads

I have rads which a best only have a drop between flow and return of 3 deg (towel rails are rubbish for this) and other T22 rads that are 8 to 9 deg  - only one rad in the house gets a drop of 10 deg and it a Triple panel, triple convector which is 1400 mm long by 700 mm high

 

12 deg is a legacy statement IMO from days of non condensing gas boilers - if you are using a condensing boiler you shouldn’t be running a  flow temp above 55 leaving the boiler - the boiler is then always in condensing mode and more efficient.

 

Now if your rads aren’t big enough at that flow temp then you have to go higher.

 

27 v 19 rads ok not as big as initially stated but still a large circuit

 

on the column rads do they all have built in diverters - if they don’t it’s normally obvious - the bottom is hot the rest of the rad luke warm

[Nickfromwales]

Thread tidied.   

 

@Dee

If you’ve got column rads then these are flow hungry, but will also bypass the flow potential of your pump (path of least resistance yaadaa-yaadaa), so basically try and draw a map of the rads and pipework in distance from pump > rad. 
Work these as an epicentre and adjust the LS valves according to % distance; eg 10 rads in a row in a straight line would have first LS set at 10% flow, 5th rad 50% flow 10th rad fully open.

 

Are all the rads fed from 15mm pipe work? 10mm to column rads is ‘no bueno’. Do you know how much 22/28mm (if any 28mm at all?) primary pipe work there is? And do you know if no more than 4 rads are fed off a run of 15mm pipework?

 

How old are the TRVs? These things don’t last forever. 

[marshian]

Screw the lock shields down to the point that the drop between flow and return on each rad is 12 deg at a flow temp of 60 and I reckon you will have a very unhappy boiler that short cycles a lot - so you will have a very high gas bill and a cold house.

 

Max number of cycles per hour should not exceed 6 but lower than that is preferred 

 

As an example - my house 13 rads currently has a boiler flow temp of 33.8 deg C and the boiler is running for 15 mins on and just circulating for 20 so 2 cycles per hour (but its all close to temp now)

 

 

[marshian]

7 minutes ago, Nickfromwales said:

Thread tidied.   

 

@Dee

If you’ve got column rads then these are flow hungry, but will also bypass the flow potential of your pump

 

How old are the TRVs? These things don’t last forever. 

Thank you for tidying the thread

 

Agreed column rads need more flow but as they have a higher volume of water content they will work well at lower temps provided they have diverters (to stop short circuit) and you accept a slower warm up time

 

Trv’s don’t last for ever - yep cheap ones are rubbish but the other thing to consider is cheap lockshields can be very non linear and make a circuit hard to balance - either get ones with a decent valve authority or go the other way and fit TRV bodies with flow control function

[Nickfromwales]

FYI @Dee, the diverters are short / medium lengths of pipe or other to make the flow enter the rad vs just skip in and out like the SAS   

Same thing you’d get with the old twin-entry valves. 
 

 

 

[Dee]

2 hours ago, marshian said:

@Dee please learn how to quote properly - write your responses under the quote of the post you are replying to - it’s horrible to untangle a mangled response where you’ve replied inside the quoted post

 

 

(Thread now tidied  )

Sorry!

[Dee]

TRVs are pegler terrier. Some are 20yrs old but I'm replacing them one by one as too costly to do all at once.

Boiler cycles 3xhr

I'm getting abetter understanding now and thanks everyone for your input