rads get red hot then stay luke warm :-(

[dazmaster9]

hi all,
i have read a few posts on this forum with a similiar problem to mine, I see there seem to be a lot of knowledgable people on here who seem willing to help, and, none of the other replies to other posts helped with my problem, so here goes.

we are not in the UK, actually in France, but we are english.

we have combi boilers (actually 2 that work together as the place we have used to be a hotel and i have turned it now into a house). all the heating except hte boilers is new. all new pipework, all new rads, all new valves, everything except boilers.

when heating comes on all rads get lovely and hot. trouble is they don't stay hot, they go luke warm, not all rads are luke warm tho, some are hot (upstairs rads) and downstairs rads are luke warm. all rads have trv fitted. i have bled, and bled and bled. I cant beleive it is sludge as everything is brand new and when ever i drain down any part for decorating etc all the water runs lovely and clear. the thermostat is calling for heat and hte boilers are fired up, some rads are hot.

i have done a lot of balancing, lock valves upstairs are only open a 1/4 turn, they still get nice and hot, in the cellar i have 3 circuits in essence as well as there are 3 floors and i put valves on each floors circuit so i could isolate/balance it there a bit, and thats all ok.

the flow pipework to the rads downstairs is hot, but for what ever reason once the rads have initially cooled down they dont get hot again, even tho the flow pipework has hot water there available.

could it be faulty trv valves? the room is NOT hot so the valves should not have closed off, it just seems strange that there is hot water there but not flowing through the rads.

my wife is giving me grief over this when in france its not quite so easy to call someone in, they rip you off if your a brit and if they have not done the work they dont want to know, and you cant afford to get them to do the work if your a brit.

all pipework is UK spec/gauge as i got it all from UK, its john guest speedfit, all valves/trv's etc are UK, bought from UK.

Its a big system with some 40 odd rads over 3 floors, but it does all work and all rads get lovely and hot when 1st turned on.

hope someone can help.

thanks in advance, sorry for waffling on

Darren

 

[dazmaster9]

hi,
after my long post it got me to sitting here thinking on it, as everything seemed to point to the trv i just thought i would pop off the trv portion of it (leaving a fully open valve) and hay ho, hot water gushing into the rads, rads red hot... so, it would seem a faulty batch of trv valves, as soon as i put the top assembly back on (and tighten down) it shuts off water straigth away, if i only partially screw the top piece on (so its sort of on but a bit wobbly) then hot water still gushes around...

so we are warm once again, wife has now stopped blaming me as i fitted it all, it was a complex big system across 3 floors and 30 rooms. woo hoo

if nothing else this post might help someone else to know new stuff can be faulty.

regards
Darren

 

[David937]

How long did it take you?
What boilers do you have?

 

[dazmaster9]

hi

the boilers are De Dietrich, 2 of them, dont have model number to hand, they aint huge ones, but they are good, have no complaints of them.

how long did it take, about 2.5 days to hang all the rads, as i said, this house is huge, 800m sq on 3 floors, it used to be a hotel, i have made a 5 bed gite on 3rd floor, 9 bedroom/bathrooms on 2nd floor and a large living area on ground floor. there are about 40 rads. it took about 4 days to run all pipework around and connect up and about another day to fill, bleed and some balancing. took another day of my planning on paper the routes and valves to isolate floors and allow me to just drain down one floor or whole system etc. i am pleased with it now i found silly prob on the trv valves.

by the way, I am not a plumber, just a handy diyer

cheers
D

 

[JohnD]

some TRVs have a Max Temp Preset on them, maybe yours do?

 

[dazmaster9]

hi
yeah, some do, but mine dont, the water flows at about 80degrees, no reason the valves should shut off after the rad 1st heats up when the room temp is still only about 17 degrees, as soon as i loosen the top trv from the body and just have it very loosely connected it all works lovely, the pin i would say is to long inside the trv body, this is of all course when the trv is open to its max (5 setting), rubbish trvs, luckily easily replaced over time when i get a moment, guess that teaches me a lesson for buying them from B&Q.

at least writting the post got me to thinking about it and a 10 minute thought process and 10 mins work lave us lovely and warm last night which won me browney points wiht hte misses

 

[D_Hailsham]

i just thought i would pop off the trv portion of it (leaving a fully open valve) and hay ho, hot water gushing into the rads, rads red hot... so, it would seem a faulty batch of trv valves

Are you getting the problem when the TRV is set to MAX or only when it is set to the desired temperature?

Did you balance the system with the TRV heads on or off?
In what order did you balance the rads?
How did you size the pump?
How did you size the pipes?
You say you have isolating valves on each floor, do you have any balancing valves?
How many room stat controlled zones do you have?

 

[dazmaster9]

hi ya

i balanced system with trv heads on, but opened to max.

rads were balanced from nearest to furthest aiming for an 11 degree difference across the flow and return.

the pump is part of the boilers and they were here already. the boilers are quite new, but the system they heated was very old cast iron, pipes running all over the walls, really upgly and industrial. i ripped out all the pipewrok back to the boilers, simplified much of it as there was an entire room/cellar filled iwth pipework and valves and i compressed that into a nice box size

i ran each circuit in 28mm for the primary circuits, dropping to 22mm and then to 15mm.

i have balancing valves for each floor, one floor is off as its a gite we only rent out in the summer, so that was easy.

we only have one room stat in the main hallway to the house. hard to site this actually as we have a log burner that i have just fitted and i have fitted an air suction/push system to this to draw warm air of the log burner hood and push around to a few of the larger central rooms (one of which is hte hallway where that stat is, but its a wireless stat, but dont know where else to put that, but thats another story.

back to pipe sizing, i based this also largely on what i ripped out.

its all working lovely now, all rads and rooms nice and toasty, just the trv valves not fully secured on the top, but they are on.

thanks for all your support.

on another note, i want to look at using solar water heating to pre-heat the rads, were we live in teh south the sun is very hot even in winter, but at night its very cold in the mountains, i think if i used solar water heating in the sun to keep the core of the house warmer then the fabric of the house would be warmer when the sun goes and boilers kick in, could this be done wiht diverter valves? where would i post this on this forum, will have to have a look wish i was a plumber.

cheers
D

 

[D_Hailsham]

i balanced system with trv heads on, but opened to max.

rads were balanced from nearest to furthest aiming for an 11 degree difference across the flow and return.

All right so far, though some advocate removing the TRV head so there is no possibility of it operating while balancing.

i ran each circuit in 28mm for the primary circuits, dropping to 22mm and then to 15mm. ... i based this also largely on what i ripped out.

Sounds OK, though the only way of getting it right is to calculate the flows along each pipe. See Copper tubes in Domestic Heating Systems and Copper in Small Bore Heating Systems.

i have balancing valves for each floor

Are these proper balancing valves, which automatically open and close to keep the differential pressure constant, for example Danfoss Balancing Valves or just gate valves?

we only have one room stat in the main hallway to the house.

With a house of that size you should really have it zoned, say with one zone on each floor controlled by a motorized valve and a wall stat. Each zone valve would be able to control the boiler.