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Cold spots bottom of radiators (40c)


Benjseb

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Hi

 

Can anyone confirm if it’s usual for large radiators that’s are running at lower flow temps (40c) to be cold at the very bottom?

 

Ive read this could be due to the flow rate rather than sludge (which I don’t think we have as these are new rads) but didn’t know if it could just be the natural drop of temp (or 40c - 5c = 35c which may feel “cold”)

 

Unfortunateoy some of our rads have the last 50cm or so piped in 8mm (from 15mm for most of the run) so that could be a contributor but it is only small sections to single rads. 
 

If flow rate is an issue is there any way of measuring the flow to see if the pump is adequate (we have approx 20 double rads running off a 40-70/130 pump on full speed). 

 

 

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It's flow rate. 

Are the valves new, and are you testing this with all the TRV's fully open ( assuming you have TRV's as new rads have been fitted )?

Can't you chop out the micro-bore and extend the 15mm pipe to the rads?

Quickest way to eliminate sludge is to turn all rads off bar one and then switch the heating on from cold. If that rad warms through evenly and quickly then the rad is fine.

How old is the pump?

Is this open pipe aka gravity, or sealed and pressurised?

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7 hours ago, Nickfromwales said:

It's flow rate. 

Are the valves new, and are you testing this with all the TRV's fully open ( assuming you have TRV's as new rads have been fitted )?

Can't you chop out the micro-bore and extend the 15mm pipe to the rads?

Quickest way to eliminate sludge is to turn all rads off bar one and then switch the heating on from cold. If that rad warms through evenly and quickly then the rad is fine.

How old is the pump?

Is this open pipe aka gravity, or sealed and pressurised?


cheers all

 

Its 2 new rads, with new valves and the pump is new. 
 

After a bit of investigation I can see the flow/return are 22mm but then reduce down to 15mm which feeds 3 rads (2 are large, 1500x600xdbl)

 

I’m guessing there’s just not enough flow from this part. Obviously wasn’t too much of an issue when it was an oil boiler

 

Unfortunately we had a new engineered floor put down in the room which has the pipe work, and a newly skimmed ceiling below too... before we decided to go with ASHP, so not sure anything will be possible to change here. 
 

 

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Just now, Nickfromwales said:

Does the ASHP drive directly into the heating, or is the heating pumped from a buffer or low loss header? 


It’s from a 100l buffer which feeds the rads and the UFH

 

Were running at 40-45c currently, so there is some scope to up the flow temp, but as it’s only one room that’s slow to heat up I wanted to try and fix that first. 

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We do have a big old barn door which has been converted to double glazed window/door but currently no curtains so there’s scope to reduce heat loss there

 

Also we have a triple window with a stone million surround. Windows within are fine, 2g, but thermal bridge on the surround is awful so will be getting a quote to replace that. 
 

so a couple of ways to reduce heat requirement, which may be the workaround!

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11 minutes ago, Nickfromwales said:

Do the rads and UFH share the same tapping off the buffer and the same pump?

Same tapping from buffer, but separate pumps. Rads have a dedicated pump then there’s a pump in the UFH manifold. That pulls 7 l/m theoretically but UFH is just two rooms and mixed down to 30 so it doesn’t pull a great deal from the buffer. Unfortunately there’s no spare tappings on the buffer to separate this out. 

Edited by Benjseb
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