Need help with Radiators cold at Bottom - not sludge

[wedge1988]

Hi All

Firstly a bit of background.

We have an Intergas 28/24 boiler, factory settings bar the min rpm set to 25 not 30.

We have just had an extension and we have added in new radiators across the house. We have gone from a 3 bed 1 bathroom to 4/5 bed (if you include the garage now an office) with 3 Bathrooms. Now, as it stands there are only 2 of us in the house and we rarely use 2 showers at the same time so we dont need a Cistern.. And in saying that it could be a future addition.

House size is about 1700-1800sqft

We took the opportunity when replacing the radiators to calculate them to be ran at DT30, so as to run the boiler at 50 degrees and return 30 Degrees, so to reduce the boiler from 65 Degrees to 50 Degrees

There are now about 16 Radiators in the house. Downstairs 8 and Upstairs 8.

Assuming most (12ish) are T22, average size is 500mm high x 1200mm wide

Now the issue:

Some* of the radiators are cold at the bottom. The towel rads get hot fine.. The T21's also cold at the bottom but only 1 or two are stone cold. If i up the temperature of the boiler to say 70 degrees, most then get warm but not boiling at the bottom, 80 degrees then they all get hot

I have tried to balance the system as best as i can. Initially 2 of the rads (furthest away) didnt warm up at all, but i closed off all other rads lockshields and they then got hot.. and since work fine.

Not sure where i went wrong with this. The plan was to add larger radiators and reduce the boiler temperature so that it takes longer to heat the house but uses less fuel (we have insulated everywhere as well with phonelic insulation on the inside of the house)

My only guess at this point is that the pump is cutting off as the boiler reaches 50 degrees. I have tried upping the min rpm to 50 and the max boiler output from 70% to 85% and this hasnt done much at all

Just need some advice really. Is the biler not powerful enough? I assumed* (yes dangerous) that reducing the temp from 65 to 50 that the boiler would still work fine but maybe it doesnt have the umph?

Any advice appreciated and please ask any questions

TIA

 

[wedge1988]

Well at some point last night i played about with the CH pump and modulating pump and all the radiators got warm, even at the bottom. id set the boiler temp to 55 degrees and had a return of 34 degrees

However i turned the pump up high to push water trough the system and now the radiators are cold at the bottom again.. oddly enough also might be caused by the single one on my landing which was off (i think) when i got them all working

Anybody have any thoughts? - im going to blast that landing one on its own again and re-bleed

 

[monkeysballs]

i have a similar issue with my setup except im running much lower flow temps 35c today (weather comp) my rads arnt cold at the bottom but they are consistently a few deg cooler than the top and im only getting a few c temp drop usually about 3.5c the pump is constantly running (or every time i check) at 60% and i think thats way too high think my highest flow requirement is 111l/h even now when the boiler hasnt been heating for 3 hours the pump is still at 60%

 

[monkeysballs]

On larger rads the bottom is about 5c cooler than the hottest tested with my thermal camera

 

[Johntheo5]

Well at some point last night i played about with the CH pump and modulating pump and all the radiators got warm, even at the bottom. id set the boiler temp to 55 degrees and had a return of 34 degrees

However i turned the pump up high to push water trough the system and now the radiators are cold at the bottom again.. oddly enough also might be caused by the single one on my landing which was off (i think) when i got them all working

Anybody have any thoughts? - im going to blast that landing one on its own again and re-bleed

Have you got two pumps, with a low loss header?

 

[Madrab]

Don't forget how rads work, hot water in, radiator releases heat, cooler out the bottom. If the differential between the room temp and rad is sufficient then the radiator will loose a lot of it's heat from the top ending up in the water at the bottom being cooler, if the pump speed is low enough then it can loose enough heat whereby the rad will be a lot cooler at the bottom.

The cooler return the better though TBH, the key is whether the room/space reaches demand temp.

 

[mcmoby69]

your boiler can provide up to 24 kw for heating rooms. my general fag packet calcs say thats enough for a 12 room house. keeping the flow temp down is good as is adjusting pump speed to make sure it gets round all the system.

have you range rated the boiler? parameter 3 needs to be set according to the heat loss calcs of your whole house, other wise it will set off at 100mph to give you a full 24kw into the radiators, get to temperature and then shut the burner off

what i have noticed is that you dont mention pipe work. is it micro bore, plastic or copper etc? all new pipe work?
did the builder plumb the rads? he wont know the 3 tee rule!

also is your boiler an ERP model or none ERP?

 

[DP]

Check the differential between flow and return of each radiator. Should be about 20 Degree C. Often the towel rails differential is almost nothing so closing the lockshield and then opening it a quarter or half turn of spindle suffices

 

[Johntheo5]

We took the opportunity when replacing the radiators to calculate them to be ran at DT30, so as to run the boiler at 50 degrees and return 30 Degrees, so to reduce the boiler from 65 Degrees to 50 Degrees

If you mean a 30deg rating (51.5% output of a 50deg rad) then you will need flow/return temps of 55C/45C.
If you want to run with flow/return temps of 50C/30C then you have a 20deg rad (30.4% output of a 50deg rad) or 59% output of a 30deg rad.

 

[wedge1988]

Thanks to all for your replies it is appreciated

i have a similar issue with my setup except im running much lower flow temps 35c today (weather comp) my rads arnt cold at the bottom but they are consistently a few deg cooler than the top and im only getting a few c temp drop usually about 3.5c the pump is constantly running (or every time i check) at 60% and i think thats way too high think my highest flow requirement is 111l/h even now when the boiler hasnt been heating for 3 hours the pump is still at 60%

Mine are mildly warm at the top and almost stone cold at the bottom, but after about 20 minutes they get mildly warm at the bottom and warm at the top, never hot all over

Have you got two pumps, with a low loss header?

Sorry not sure, i dont think so..

your boiler can provide up to 24 kw for heating rooms. my general fag packet calcs say thats enough for a 12 room house. keeping the flow temp down is good as is adjusting pump speed to make sure it gets round all the system.

have you range rated the boiler? parameter 3 needs to be set according to the heat loss calcs of your whole house, other wise it will set off at 100mph to give you a full 24kw into the radiators, get to temperature and then shut the burner off

what i have noticed is that you dont mention pipe work. is it micro bore, plastic or copper etc? all new pipe work?
did the builder plumb the rads? he wont know the 3 tee rule!

also is your boiler an ERP model or none ERP?

The boiler has 2 options on c and c. - c is the CH rpm speed and c. being the modulating pump, there seems to be a fine balance between them in (c) gettig the water hot through the boiler plate and (c.) pumping it around the house? - please correct me if i am wrong this is my understanding..

I have set the Boiler to 100% for (3) - 23~24~kw and the rads are all summing up to about 22kw. The dual thermometer i have on the flow and return on the boiler show 50oC out and 34oC return when (c) set to 50 (max) and (c.) set to 75 - i am trying to improve this

Pipe work comes out the boiler at 22mm copper and splits off into 15mm copper and plastic pipe, which the downstairs and upstairs are fed through the ceiling, down the walls etc - and all new pipework bar 1/3rd which is the 15mm copper

The Boiler was moved and re-installed by a gas engineer though, also supplied the signed paperwork etc

Boiler: https://theintergasshop.co.uk/intergas-boilers/211-intergas-combi-compact-hre-28-24-049568.html
Docs: https://www.intergasheating.co.uk/homeowner/products/hre/hre-28-24/documentation/

93% ERP?

If you mean a 30deg rating (51.5% output of a 50deg rad) then you will need flow/return temps of 55C/45C.
If you want to run with flow/return temps of 50C/30C then you have a 20deg rad (30.4% output of a 50deg rad) or 59% output of a 30deg rad.

I'd like to run it lower but i calculated the rads based on 50 degree flow for 21 degree room temp..

Anybody know why the rads are still cold at the bottom? I find it strange.. I would still expect them to get hot. I will start to balance for that magic 11 degrees across them next too

Is there a way for me to calculate the settings needed or is it just going to be play with it and see

Thanks all!

 

[desktop987456]

I am not a pro but DiYer like you; how rads closer to the boiler are performing? Do they get hotter than rads further away from boiler.

 

[Johntheo5]

I have set the Boiler to 100% for (3) - 23~24~kw and the rads are all summing up to about 22kw. The dual thermometer i have on the flow and return on the boiler show 50oC out and 34oC return when (c) set to 50 (max) and (c.) set to 75 - i am trying to improve this

You say all the rads are summing to 22kw, if this is based on the normal 50 deg rad rating which is the mean rad temperature minus the required room temperature then when/if you run the rads with flow/return temps of 50C/34C with a required 21C room temperature then you will have, (50+34)/2 minus 21, a 21 deg rad which will give (21/50)^1.3, 32.4% of its 50 deg rating or a total output, in your case of 22X32.4%, 7.13kw. If you are happy with this then fine or else you may have "oversized" the rads by a factor of 100/32.3, 3.1. I can certainly post a S.sheet with calculation method of the flow rates required for any given rad(s) outputs.

when (c) set to 50 (max) and (c.) set to 75 -

Can you post the exact info on this please.

The main reason for cold rads at the bottom is sludge build up, hardly a problem with new rads though.

 

[wedge1988]

You say all the rads are summing to 22kw, if this is based on the normal 50 deg rad rating which is the mean rad temperature minus the required room temperature then when/if you run the rads with flow/return temps of 50C/34C with a required 21C room temperature then you will have, (50+34)/2 minus 21, a 21 deg rad which will give (21/50)^1.3, 32.4% of its 50 deg rating or a total output, in your case of 22X32.4%, 7.13kw. If you are happy with this then fine or else you may have "oversized" the rads by a factor of 100/32.3, 3.1. I can certainly post a S.sheet with calculation method of the flow rates required for any given rad(s) outputs.


Can you post the exact info on this please.

The main reason for cold rads at the bottom is sludge build up, hardly a problem with new rads though.

Great reply thank you!

Apologies about my beginner level understanding, i am learning still

I see.. then i may have oversized the radiators a bit too much? I calculated the radiator size by finding the BTU needed for the room based on the BTU output of the rads at Delta T50°C.

So essentailly the radiators are 3.1x the size i needed? oops.. I was planning on running the boiler at 50 degrees and aiming for a 30 degree return (20 out to the room)

But i could reduce the boiler further from what you are saying?

Sorry if i dont understand.. i'm trying

No problem; the doc is here; https://www.intergasheating.co.uk/a...-Compact-HRE-Installation-manual-88287806.pdf

(Page 40 param c and c.)

All rads are new and all piping bar 1/3 of the older piping, no issues before though. Radiators do get warm at the bottom if the boiler has been on long enough, which would suggest that its just a matter of being patient

thanks and regards

 

[Johntheo5]

I see.. then i may have oversized the radiators a bit too much? I calculated the radiator size by finding the BTU needed for the room based on the BTU output of the rads at Delta T50°C.

If you sized the rads based on the manufacturers definition of a T50 rad, which I think you did, then all I am saying is that if you wish to run them at a flow temp of 50C and a return temp of 30C to maintain a room temperature of 21C? then the rads will "only" emit 28.4% of their T50 rating or a total of 6.25kw which may well be enough to heat your house depending on insulation etc and depending on the outside airtemperature. n

No problem; the doc is here; https://www.intergasheating.co.uk/a...-Compact-HRE-Installation-manual-88287806.pdf

(Page 40 param c and c.)

All rads are new and all piping bar 1/3 of the older piping, no issues before though. Radiators do get warm at the bottom if the boiler has been on long enough, which would suggest that its just a matter of being patient

thanks and regards

 

[wedge1988]

If you sized the rads based on the manufacturers definition of a T50 rad, which I think you did, then all I am saying is that if you wish to run them at a flow temp of 50C and a return temp of 30C to maintain a room temperature of 21C? then the rads will "only" emit 28.4% of their T50 rating or a total of 6.25kw which may well be enough to heat your house depending on insulation etc and depending on the outside airtemperature. n

Ah ok this is great to know thank you - yes i sized them based on T50 rads

I have well insulated the house, we have a new extension on the back and the rest i have battened out the walls and applied 50mm phenolic board so it gets nice an toasty.

The settings i have on the boiler at the moment - the boiler flow gets to about 45-48 degrees (set to 50 on the display) and return of about 30-34. I am finding that reducing the modulating pump speed or boiler speed that it gets to 50 degrees too fast and shuts off well before the room temperatures are up to where they should be, so i assume in this case i need to tweak it so that the boiler doesnt turn off but try and get the best Delta T return such as 48/28

Would there be any benefit (bar the longer warm up time) or trying the boiler on 40/20 ? - if the rads are bigger than i expected is this possible?

Also feel free to share the excel sheet with me? I am learning still but would like to check it out

Thanks again!