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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Dead legs and central heating circulators https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1222884414 Message started by runninwata on Oct 1^st, 2008, 7:06pm

Title: Dead legs and central heating circulators
Post by runninwata on Oct 1^st, 2008, 7:06pm

Here goes!! Have installed a Grant vortex 36/46 condensing oil boiler, supplying a 4 bed house with 11 rads with a 15/60 grundfos pump, unfortunately 4 radiators which were added at an earlier date when the house was extended are not heating.

The radiators all heat when i crack open the valve without one of the radiators in place and drag the water through to them which leads me to believe the circulator isnt fit to cope with the job,

I have tried balancing the system and shutting down the rest of the house and only bringing these rads into service but all to no avail.

My question would be is there any light commercial circulators available that would be stronger than this grundfos 15/60 pump but would still fit into the 130mm port to port dimension or will i have to go for a commercial flanged pump and re jig all the pipework

any help and advise greatfully received

Steve

Title: Re: Dead legs and central heating circulators
Post by thescruff on Oct 2^nd, 2008, 1:40am

I would think if the 15/60 don't shift enough water then you have a system problem.

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 2^nd, 2008, 7:52am

System problem? maybe but the system was heating ok before the boiler swap and pump swap, the old boiler was pumped using a 15/50. :o

I am goin to check pump resistance again as i cant understand that it all worked fine previously, only other thing i was thinking about was a blockage somewhere but that seems unlikely as when i crack open valves without rad the others in this leg heat evenly and ok confused I am!!

Is it possible to get a F :ocked pump straight out of the box?

regards

steve

Title: Re: Dead legs and central heating circulators
Post by CWatters on Oct 2^nd, 2008, 8:45am

Re the balancing.. If shutting down the rest of the system totally didn't cause at least one of the four to heat up then something is wrong with those four. Air lock? sludge? Incorrect plumbing? The pump should be able to push water around.

Not wired in series are they? Perhaps just the one you removed is blocked?

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 2^nd, 2008, 12:54pm

No, I have removed each of the four rads and cracked the valves at each of the points and the others have begun to heat up as soon as rad re instated the rads then cool, system was flushed prior to instal and has been drained and re filled twice since, initially thought airlock but have had aav installed in leg to these rads ,magnaclean installed also and is remaining pretty clean since installation just minor debris!!

I am going to double check everything is off and isolated other than these rads and will update later

cheers for the advice

steve

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 4^th, 2008, 12:49pm

Hi, checked pump resistance was ok, double checked isolation of all other rads, allowed problem rads to call for heat, lifted landing floor (much to the annoyance of swmbo ::) ) to access flow and return that supplies this side of the house flow gets hot but nothing on return side,
cracked open valve without rad on and rads begin to heat, I am goin mental!! contrary to what my trade is I AINT A PLUMBER! :'( The installer unfortunately is out of the country on hols at the moment and can not be contacted either!!

Anybody any other ideas, if it is a bockage could this just be flushed by breaking a joint underneath and flushing each of the flows and returns at each of the four rads?

Help

Steve

Title: Re: Dead legs and central heating circulators
Post by bill577 on Oct 4^th, 2008, 9:22pm

it sounds like you have a block on the return, but before you hack into the pipework, check the pump is installed the right way round, believe me it does happen ;)

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 7:06am

cheers lol i will check this out this morning!! its gettin really cold here now and mrs isnt happy about the fact that we spent approx 4kon boiler and unvented and half the house is colder than it was with the old boiler!!

thanks

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 1:13pm

Do any of the radiators heat up or is it just these 4?

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 7:27pm

Hi Greg,
rest of house heats up great, only these four no heat at all, they were installed as part of an extension.

regards

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 7:37pm

What happens if you shut of the valves to all of the radiators in the house except 1 of the 4?

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 7:50pm

Hi greg, tried shutting down all the system except these four then all these four in turn still none of them even start to heat, there is a slight warmth at the valve on the first rad in the extension but seemingly no circulation, i have had this rad off and flushed through water was clean nothing amiss,

regards

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 8:11pm

I take it that it is a 2 pipe system and that the flow and returns are connected correctly?

How high are the rads above the pump?

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 8:14pm

It is indeed a two pipe system and the rads would be on the same level or thereabouts as the pump

regards

steve

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 8:16pm

flow and return connected correctly, was all operational before boiler swap and adding of 2 extra rads 700 x 300 and 700 x 600 k2s all bi directional valves

regards

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 8:22pm

A 15/60 should be OK. Are the tails to the rads getting hot? You say you have had the floor up, can you trace the pipes back to where they connect to the rest of the system that is heating OK? If you are getting no circulation it will most likely be an airlock, blockage or piping error ie flow and return are connected together

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 8:36pm

yes had the floor up to install two aavs (initially thought airlock) on the leg just as it enters a wall to drop vertically to serve this leg with 4 rads on it,

No only one of the tails is getting hot, (the first rad in the line) the rad doesnt get hot and the other 4 rads are stone cold along with Mrs! lol

Have just managed to speak with installer, he says he thinks the pump could be struggling! I am now doubtful and believe blockage, it worked previously with the old boiler and a 15/ 50 pump, would it do any harm upgrading the pump to a commercial type or is that money wasted.

is powerflush best way to remove blockage or could i do it by removing rads, draining system , connecting hose and mains cold water then opening valves in turn on problem rads with all other rads isolated to flush out blockage?

your help is greatly appreciated

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 8:51pm

Are you able to do a drawing of the pipework layout? Its difficult to see it in the minds eye.

If you go to next pump up from the 15/60 then you are into the magna range if i remember correctly and you will be looking at a couple of hundred quid and im still not convinced the pump is the issue, ive used 15/60's on 3 story houses with 14 rads with no problems what so ever.

Is it a sealed system or open vent? Does the pipework have any rises / drops in it before these rads? Can you definitively trace the flow and returns that they haven't been crossed over anywhere? Are there any valves in the pipework?

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 9:12pm

It is an open vent system,

Pipework drawing difficult as can only just do two finger typing on the pc lol

Pipework has not been altered other than installing motorised valve as went for unvented cylinder and previous boiler was on single channel timeclock!

boiler is housed externally in insulated purpose built room Pipe work rises from boiler onto first floor then along landing to first floor rads (4x)drops down walls in three positions at either side of house to serve ground floor rads (8x)

first floor 4 x rads all heating

ground floor 4 x rads heating
4 x rads stone cold they are on the leg that i can feel the flow is red hot as it enters the wall (return is cold)

only valve other than the motorised valves that was added to system was an auto bypass valve.

the flow and returns were never altered boiler was swapped rads added back to back with existing rads to eliminate cold spots on landing etc

i aint really worried about the cost! just as long as it works and we are not cold lol

Old boiler was a 15/ 19 worcester which was never upgraded as the house was extended twice Mrs was freezing last winter I am expecting divorce if she cold this winter!!

regards

steve
regards

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 9:31pm

The rads are filling Ok with water, both directions?

If the system worked before and there have been no pipework alterations then it deff sounds like either an airlock or blockage.

The fact that turning off all the other rads has no effect from what i can understand from your posts shows that its not the pump, it is pumping the right direction?

Are you able to drain the system and cut into the flow and return serving these 4 rads and connect hose to see if you can get flow through?

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 9:38pm

Rads all fill ok from both directions, when one of the cold rads removed and valves cracked open rest of cold rads warm up ok,

pump is pumping in right direction.

would i be right in saying that to cut into the leg serving these rads i need to cut a tee into both flow and return with iso valves then open up when filled and calling for heat to see if heated water flows? I aint a Plumber by the way!! lol

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 5^th, 2008, 10:09pm

Quote :- when one of the cold rads removed and valves cracked open rest of cold rads warm up ok,

bit confused by this

if you drain the system down completely, cut into flow and return serving these 4 rads, attach one end of hose pipe to the flow pipe, other end to outside tap. Connect another hose pipe to the return pipe and run to outside. Make sure the hose pipe connections to pipes are good, you don't want water going everywhere ;) The 4 radiators still conncected, valves fully open, remove TRV heads if needs be. Turn on tap. In theory water coming out of the return pipe should be equal in terms of volume / pressure as what it goes in. Whilst water is running through, bang the radiators across thier surface with rubber mallet. How clean is the water coming out? If all seems to be flowing OK rejoin the flow and return pipes.

When is the original plumber back off hols - bit naughty that he left the system like this

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 5^th, 2008, 10:20pm

Quote :- when one of the cold rads removed and valves cracked open rest of cold rads warm up ok,

bit confused by this

confused you need not be ;D lol

when heating on, remove one rad on circuit, open valves into bucket seperately and slowly in turn, lol rest of rads at this side of house get red hot! (Like i said I am not a plumber) ( cheers lec!)
all rads have been of and flushed through independently and water clean,

Plumber back sometime next week, he is a friend and wasnt aware when he left that the system wasnt peforming as it should unfortunately he balamed the pump when i called him earlier.

regards steve

Title: Re: Dead legs and central heating circulators
Post by CWatters on Oct 5^th, 2008, 10:52pm

Is it possible flow and return got swapped and the TRVs are unhappy about this? Perhaps removing a rad and opening a valve is chaging the pressue enough for them to open?

Title: Re: Dead legs and central heating circulators
Post by qwertyman on Oct 6^th, 2008, 9:38pm

Do the Radiators have TRV`s on them?....If there is hot water to the valve but not entering the radiator it could be that the thermostats are stuck in the off position.To check this - unscrew the TRV cap and you should see the top of a pin sticking through.Lightly tap the top of it until it "pops" up into an open position.Water will now pass into Rad.

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 7^th, 2008, 9:33pm

100% sure flow and return not reversed, TRVs not faulty, nHave spoken with tech rep for grundfos and confirms pumps is satisfactory for what i am requiring. so.. Have organised powerflush unit for the weekend with the installing plumber, will post further details after flush.

thanks

steve

Title: Re: Dead legs and central heating circulators
Post by greg on Oct 8^th, 2008, 10:28pm

OK m8 hope you get it sorted, let us know

Title: Re: Dead legs and central heating circulators
Post by runninwata on Oct 12^th, 2008, 1:49pm

Just an update, powerflushed system twice for a total period of about 4 1/2 hours or longer! No improvement! so..... Much to the annoyance of Mrs, lifted carpets created hatches and lifted flooring to discover the following,

Extension which was built approx six years ago had been completely piped in Non Barrier hep pipe, The flow off the tee from the last rad that was getting partially hot was completely choked approx 2.0m length solid of sludge particles etc! powerflush didnt even get near it, Cut into system removed this leg of pipework and established circulation again by connecting hose and opening each rad in turn until good flow received in each.

However have set a date to get the extension completely re piped so as there is no doubt.

Cheers everybody for your input it was greatly appreciated

Just goin to re lay floor before i get a divorce

Cheers

steve

Title: Re: Dead legs and central heating circulators
Post by CWatters on Oct 16^th, 2008, 8:23pm

Glad to hear it's sorted. Don't forget the corrosion inhibitor once the system is finished.