Central Heating Flow pipes burning hot - Return Pipes cold

[doitmyself]

Hi Gas Engineer: - Whole Story so far: ...They did not flush the system when new boiler went in. ... Switched on - Circ Problem happened straight away.

At least you haven't paid the chap.

Another plumber in ... balanced rads

How was he able to do this if the return is cold?

You say that, if one rad is turned on at a time, it heats up OK but the return pipe is still cold. Have you checked that the lockshield valves are not closed?

You say that all 22mm cooper pipe has been replaced with plastic and the problem is still there. This would suggest that the problem is elsewhere.

If you disconnect both ends of the plastic pipe where it joins the rest of the system, close down all rad valves, connect a hose to one end of the plastic pipe and send some water down the hose, you will be able to check if the plastic pipe is clear. If it is, you will know the blockage is not in the plastic pipe and must be in the rest of the system, i.e before or after the plastic pipe.

 

[lewisplumber]

Are the rads on drops from the loft or are they under the floor? And just wondering if the rads have been bled? Stupid questions but these things are over looked.

 

[RTPS]

Have you got the flow and return the wrong way round on the boiler? just a thought
Also negative and positive pressures do not apply to a sealed system!

 

[tamz]

Generally in Scotland the houses all have solumns so most likely all under the floor.

 

[doitmyself]

Generally in Scotland the houses all have solumns so most likely all under the floor.

What's a "solumn"? Is it a Scottish word for cellar?

 

[tamz]

You would need a strong back and some big rawlbolts to get a camray on a wall.
F&R is irrelevant.

 

[tamz]

What's a "solumn"? Is it a Scottish word for cellar?

The space under a suspended wooden floor.
A cellar is just a cellar but it is like a cellar for midgets 😀

 

[doitmyself]

The space under a suspended wooden floor.
A cellar is just a cellar but it is like a cellar for midgets 😀

Did a google for "solumn" and it asked if I meant "solemn"; so I said no. I then had to trawl though many search results where the word was a mis-spelling of "solemn"! But I eventually found a relevant one; the specification for a building in the Shetlands!

 

[tamz]

Well now you know😉
It probably is a Scottish word as everyone up here knows what it means. For those who don't,

Solumn: The space under a suspended wooden floor (crawlspace).

 

[gasmarc]

this is an interesting thread I suspect it is something really simple that has been over looked ,if they are getting hot water that proves the pump and boiler are working correctly, I would cut the flow in the middle and run a length of hep to the return , if it gets hot you know the problems on the return pipe, i did have a similar problem before years ago where all the rads had been replaced but for the life of me I could not get the rads permanently hot, I must have spent over a week back and fourth with the boiler manufacturers coming out every few days also, they had recommended putting an extra pump on blah blah blah ,All this turned out to be rubbish as the boiler was wired incorrectly internally ,

 

[TheGasEngineer]

... Also negative and positive pressures do not apply to a sealed system!

Oops forgot it's sealed. Actually there is negative and positive head even in a sealed system. I think, it's just half the pump head; negative up stream and positive down stream. If there's vent it can be negative to the value of the whole pump head if the vent is down stream and likewise positive the whole pump head if the vent is upstream. In the former case this occurs if it's a small static head and is the cause if ingress of air which "mysteriously" builds up in radiators suffering the negative head.

There is another possibilty - air locks. I get quite a lot of work from doing small re-pipes and fitting vents. Even in sealed systems, an inverted pipe loop without a vent can stop any system working.

Trace all pipe runs. Once it starts going up hill start looking for the high point ie just where it starts going down hill again. There must be a vent at each high point.

A "good one" I find is a wall-mounted boiler with flow and return on the top. The pipes come up from the floor, go over the boiler and drop down to the F&R couplings creating a couple of lovely air locks.

 

[tamz]

It is a camray oil fired
Greenstar Camray External 18/25 - Worcester, Bosch Group UK homeowner site
The house is a bungalow and the pipes below the floor

 

[TheGasEngineer]

So the high point for the boiler will be the vent at the top of the heat exchanger or there abouts. I would recommend that and the remainder of the sytem is checked. There is no doubt that airlocks would cause this problem and if the plumber does not understand their significance they could be everywhere...

 

[tamz]

The cylinder is 12 meters away from the boiler and the water heats fine so no problem with air at the boiler or the cylinder (prepiped module). The problem lies with the circulation through either the module or the heating which is below the floors. It is not air.

 

[Jodi Thomson]

Yeah that the correct boiler tamz

 

[Jodi Thomson]

Hello Folks

OK - Plumbers in this morning, checked all again, no blocked pipes. Put the spare 15/60 grundfos pump onto the return line - small change - can get most rads to heat bar 3. Any other ideas?

 

[ToolGuy]

Does the system have two motorized valves, one for the CH? If a radiator is starting to get worm but return is still cold it could be the hot simply hasn't yet replaced all the cold in the radiator. Then boiler is overheating so cuts out. No pipe blockages found. Might be a time/temperature problem with CH motorized valve. It gets warm/hot and electric motor coil opens and it shuts hence intermittent blockage only when hot.

 

[Jodi Thomson]

The Motorised Valve has already been checked and this is not faulty. All the rads in the house are now hot except the two up the stairs, but i am not bothered about these at the moment. The rads have taken about an hour for all to become hot. This seems like a very long time

 

[Toddyplumb]

Now is the time to start balancing , as long as you are happy with flow

 

[Jodi Thomson]

ok dokay - The plumber has told me to leave all rads on full blast and he will be back on wed am to check them.

I prefer the bedrooms to be quite cold as these are only used once or twice a year, and the living areas to be warmer. Should i open the living areas fully and close down the rooms that are not used, or should i do it by the sequence the rads come on i.e. closest to the megaflo closed off and open come the end rad?

 

[GrahamM]

Essentially you want the Lockshield valve on the furthest away radiator open and slightly close them more and more as you get closer to the pump. This will balance the system.
It takes a bit of practice to get this right and is quite important if you want the best out of your system.
If you don't want as much heat in bedroom then you control this by opening and closing the TRV's to your requirements.

 

[robbin]

Did you ever satisfactorily resolve this. Re - your 2 pictures - is the grundfos mounted vertical as in pic 1 or horizontally as in pic 2.

 

[kkr]

Theres a story about the old penny trick ? usually when a custard has nt weighed in the plumber properly ? 🙂 Id say track the flow and return til you spot the temp differ. to find the blockage ?

hiya

I was the plumbers apprentice today. We did use FX2 and we did each rad seperate at first whilst hitting them with a mallet, then did them all together for one final blast, it didn't shift the blockage at all. Whilst flushing each rad we listened for flow in the rads, and each rad seemed to be getting. Turn it to CH mode and the return pipe gets boiling hot to touch, boiler runs for 2.37 mins and cuts off, and return pipe flow dosn't seem to go anywhere. The plumber doing the works now, was not who installed it. The installed has done a runner and we can't get hold of him to rectify the fault, so were having to pay out even more money to get the original fault sorted. Our new plumber has said to leave the CH on full blast for the whole weekend, and he'll pop in past again Mon am to see if theres any change. This system was fitted in March and has never worked, but it wasn't such a problem in the summer months, now it 0 deg c here in the northof scotland and were freezing! thank god we have a gas fire or we'd really be us the creek without a paddle!!!!

 

[khill]

Old thread I know but a couple of my own experiences with regards
situations like this. Its so easy when cutting a chopping old bits to new
bits to leave little bits of exsistng here and there due to being difficult
to get to, boxing, trying to save the customer some decorating
etc... One situation I had very simular to this was I spent hours on
an installation only to find a couple of old checks valves (non return)
on the old exsisting pipework and due to the re routing of pipework
they were now facing in the wrong direction, this were only found
after taking down boxing.

The other time and some thing that has taught me a good lesson
...."Good house keeping".... do not put all your fittings in one bucket,
as 15mm end feed caps have habbit of getting stuck inside other
fittings....lol.... I could have kicked myself.

 

[stevetheplumber]

ive had a piece of tube go past the stop on a tee effectively blocking the pipe sods law it was the lowest point of the system under a floor