Last rad cold at the bottom - bit of an odd one as I don't think its blocked...

[M7R]

The last rad in my system, the down stair hall rad, seems to be showing signs of being blocked... but I don't think it is.. heres the info...

The system was installed by the neighbor in the late 60s early 70s, (neighbour still loves next door, they have been in since the house was built in 56!)

it did have a Baxi Bermudia back boiler system, we still have the fire but about 4 years ago while the last owner was in she had a new Vitedons W100 boiler fitted in the bathroom..she had it fitted due to being a pensioner so got it on a grant I believe.. at the same time the boiler was fitted the back boiler was by passed next to the boiler, and the bathroom rad was put on its own loop.

when we moved in 2 years ago I removed all the rads bar the 2 curved ones in the bays (which are going this summer to be replaced by 2 doubles on the other wall as getting 2 curved rads is stupid money!) and replaced them with rads from Wickes, along with adjustable and fixed length adapters to convert the imperial length old rad spacing to slightly smaller metric rads.

I dont know if it has been like this from day one, but certinally for the last 6 months, the hall rad which is the last on the loop and a new rad seems to have the issue of the hot water coming in, going up the first 2 water jackets, and the top being hot, and thats it.. the middle is warm, and the bottom is pretty much room temp, even only 3" from, the inlet!!! (the outlets never red hot either!)

Last weekend I cleaned out the header - see my other post for the mushroom farm I had gown in less than 2 years in there!!! - and filled the system with Sentinal X800 cleaner, which has had a week to work its magic! the rads used to bleed clear, but after I messed around with the system they started to bleed charcoal...emptied, refilled the system and added the x800, and over then today with a mate I dried the system again, wiped down the header (charcoal water but no rust bits etc in there..) and then took off the hall rad, flushed it through with the hose, via the bottom inlets and the top where the blank and vent should be.... when blasting the water through the inlet it came out of the outlet pretty quick, like it was just running along the bottom water way and not up, along the top and back down! it was black-sih for the first few second then charcoal and then clear pretty quick.

we also did the old bay rad before it, got some black water out of it but not masses...

Then we refilled the system with clean water, bleed all the rads, kicked the pump in for 10 mins on high to dilute any crub in the pipes we couldn't get out (with the hall rad locked off to stop any crud going in there)..after 10 mins, drained again, and it was pretty clear really...

then refilled with another shot of X800, the heating has been on for a few hours now, pump on speed 3 as it says and the hall rad is as before, only hot on the top and the first couple of water jackets.. I have been and balanced the system but its made no odds..the old bay rad which is before it red hot top to bottom all the way along, as are the others...

so what do people think? I have even tried hitting the rad at the bottom with a plastic hammer encase there is any crud stuck and the vibration will dis lodge it.. but it doesn't seem to have made any odds...

The rad is a single 1450mm, if that makes and odds, and I am sure it is the last on the loop..

any help of suggestions would be apprecaited, the hall isnt that cold... but it bugs me its not right as all the heat goes straight up the stairs, and I am a bit OCD about things being right..

Cheers

Karl

 

[M7R]

No that's what I'm saying this is a new rad, it's only 2 years old. There only 2 old rads left one up stairs in the front room as its a curved rad in the bay, and the same down stairs, the curved rad is the one before this rad... But logicly that shouldn't make any odds? Unless its higher water content means more water is going into the bay rad then back into the return loop..

 

[michael c]

Definately sounds like a return restriction, you may be able to drain the return feed but that doesn't mean there are no restrictions. Remember each rad is on individual legs and any restriction the majority of heat will take the easy path. I would bet that the restriction is in the pipe and not the rad. You need a proper flush or it may be cheaper in short term to replace the leg. Its my opinion that your wasting your time keep flushing the rad.

 

[M7R]

Okay, power flush it is then once the new rads and pipe work in the bedroom and dining room have been done... I'm lothed to replace that leg of pipe due to the new floor that was laid only a few months ago... Cheers

 

[michael c]

Okay, power flush it is then once the new rads and pipe work in the bedroom and dining room have been done... I'm lothed to replace that leg of pipe due to the new floor that was laid only a few months ago... Cheers

Is there no way to get under the floor?

 

[M7R]

When the heating was installed the neighbour has told me that in the back room there are a few floorboards which are lose, this is where he got in to the crawl space under the house.. The one hall rad is as far away form there as you can get...

but there is news! This morning I have turned off all the rads, turned down the bathroom rad as much as I can without causing the boiler to lock out after a couple of mins, and with the pump on 3 you can hear the water racing through the hall rad! I have left it running for 20 mins while I do other stuff, and now just turned the boiler up to 70deg, gone down stairs and the hall rad is hot top to bottom all the way along.

i am coming to the confusion that the 2 bay rads are robbing too much water, they have to be neary all the way open to get an even heat and they hold a lot of water! I think this is allowing too much water to short circuit back to the boiler before getting to the hall, and that joined with the fact the hall is a big long rad means the water that is making it there is not enough to heat the full rad. However I will leave it running hot with just that one rad open for another hour or so as it won't do any harm to clean those pipes through

 

[tolly]

When you next take the rad off get a bucket and an old washing machine hose. Screw one end of the wash mac hose onto the rad valve and put the other end into the bucket and open up the rad valve. Check to see that the water flows freely into the bucket and this will tell you whether there is any blockages in the pipework feeding the rad.

 

[tolly]

Do so on each of the rad valves

 

[M7R]

Ok will do next weekend when we whip it off again, it seems to be flowing really well now though all the others are turned off,

 

[michael c]

Tolly gives good advice there mate, i would expect the rad to have flowed as only route now it does sound though that your bay window rads need restricting

 

[CM25]

Sounds like a circulation problem to me not the rads as it's hot hot all over when uve shut everything off
Check if a bypass is fitted and ensure its not fully open, does the problem occur all the time or just when heat and hw on? If this is the case a balancing valid on hw rtn maybe req, do u have a combined air/dirt separator for the cold feed and vent cos I've know them to get blocked, check the pump, if the systems old it can block/restrict the unions on the pump but the pump appears fine.
Hope this helps but definitely sounds like a circulation/balancing issue not the rad

 

[M7R]

The pump is as old as the boiler, I have stripped and cleaned it as it got blocked on the last clean due to the crap x800 which had been frozen... Cleaned and cleaned the system, all is good. The pipe work Round the boiler and pump is new too as it was all changed when the boiler was added.

hw balance is only 1 and a bit turns open, but the problem is the same even when he is not demanding heat and the valve closed.

i have balance the system again and the problem is back, I'm sure the bays are t helping, as they have old valves where it's only one turn from closed to open, both are set about 1/2 open or just under, this is where the inlet is very hot and the outlet is just warm to hot.. So a out right, the rest of the rads are about the same with the valves being new and about 1 to 2 turns open apart from the hall which is wide open.

 

[CM25]

How bout the bypass it's btwn the pump and the 2/3ports and goes straight to the rtn, and if this is too open it'll short circuit back to the boiler

 

[CM25]

Also check the cold feed/vent arrangement, if uve got a combined one its possible it's blocked. Where's the hall rad that's fully open in relation to the one that's not working, and waters lazy an it'll take the easiest path.
Just to confirm if the other rads are off the problem rad is hot all over?
Still sounds like a circulation fault tho

 

[M7R]

I have a separate vent and feed, when we drained and refilled the system the vent was gurgling and spitting water every so often so I know that's clear.

the problem rad is the hall one, is the last on the loop and a 1.4m single, which comes after the 1.4 old rad in the dining room bay, a big old rad with out fins, -this is being replaced in a couple of months, along with the old bay rad in our bedroom.

if its still a prob after the other 2 old rads have been replaced then ill be annoyed..

 

[StillLearnin]

Have you considered pressurising the system, that bit of extra pressure might help the flow a bit.