pressure dropping on central heating

[rooter75]

hi all,

ive been looking on the site for some answers (excellent site btw) but can't find the right answers, so here goes:

i heard one of my ground floor radiators gurgling so decided to bleed the air out of it. i did this gradually and kept on checking the gauge under small red 'tank', topping it up to 1bar as i went. got all air out of radiator and everything seemed fine.
however checked the pressure again the other day and it had dropped to just under .5bar while cold? i topped this up to 1bar again, ran the system and it got to about 1.4 bar when hot?
then i left it overnight and it dropped to about .8 bar, however when i turned heating on the pressure dropped to about .2bar straight away before rising to about 1bar.
ive turned it off and its currently sitting at about .9 bar, while warm but not turned on?
any suggestions?
i have an ideal/icos he18, with megaflo unvented/indirect tank, with a small red tank above it with the pressure gauge. i have 14 rads in total

sorry for the long post, just trying to give as much info as possible

rob

 

[aqualogic7]

if you have 14 rads and a small expansion vessel could be under sized expansion vessel follow link it will give you a chart for sizing http://www.idealheating.com/downloads/manuals/203318_inst.pdf

 

[rooter75]

hi and thanks for reply, so the red tank is an expansion vessel?
it has 12l capacity and maximum working pressure of 4bar.
should add, the system was installed in a new build nearly 5 years ago.
have checked everywhere thats visible for leaks, can't find any evidence.
would any pipes have been installed in the concrete floors on ground floor?
seems as though all pipes to radiators run inside the stud walls?

 

[wheeto]

If the pressure is only reaching 1.4 bar when hot then I doubt an under-sized expansion vessel is at fault here. Think you just need to find a leak! Options are pipes feeding radiators, the radiators themselves, the boiler (sometimes a leak in the boiler will escape through the flue as vapour so you can't find it!). You can rule out the cylinder coil in this instance because it's a pressurized item.

Pipes buried in screeded floor can be traced by the heat they give out.

 

[rooter75]

thanks, currently looking for a leak!!
what should the pressure be at when hot? i don't recall it ever getting much above 1.4-1.5bar?
this is a bryant home, which were taken over by wimpey, so i doubt if i will be able to find out if pipes were located in the floors. the plumbing company which installed the system went bust last year :sad:
just been feeling around the ground floor and can't feel any dampness or heat

 

[gas46]

hi have you checked outside it may be prv off the vessel that is passing, pipe should be dry any signs of discharge and thats your problem

 

[rooter75]

hi gas46, what is a prv? sorry for the ignorance!!
i went outside the house to see if there were any overflow pipes dripping, and guess what? all pipes must run inside the walls and into the ground via a waste pipe or something because there are know pipes coming through walls to the outside?

 

[gas46]

hi there will be either a pipe normally 15mm that runs to an outside wall or alternately you should have a tundish somewhere around the cylinder looks a bit like a small funnel inbetween two pipes as you have an unvented cylinder they may be joined together these are to prevent pressure build up should water get too hot as there is a risk of serious scolding or even worse

 

[rooter75]

ah, no pipes to outside, but there is a black 'open' plastic thing between 2 copper pipes, next to the megaflo.
there is a little drop of water dripping through this about every 10 seconds.
could this be the problem?

 

[PlumbBobBob]

certainly sounds like it. shouldn't be any discharge at all. you will need to get an engineer qualified to G3 to do a service on your unvented cylinder.

 

[gas46]

yep the black plastic thing is indeed the tundish if its dripping thats the prob

 

[warrington]

as steveb says, you need engineer with unvented ticket, as there are several reasons for that, your engineer will find it.

 

[rooter75]

thanks everyone, hopefully i can get this sorted out asap.
is this tundish thing the overflow? because the megaflo has a sticker on it, explaining how to regenerate the internal air gap if overflow is dripping?

 

[gas46]

hi dont think its the air gap in the cyl as you are losing pressure from heating side but like the man says you need to get a engineer to have a look

 

[PlumbBobBob]

it might just be the expansion vessel needing recharging, but it might not. you really need a qualified engineer to look at it imho.

 

[rooter75]

thanks again guys.
can you recommend anyone from the bishop auckland area who could do this?

 

[PlumbBobBob]

rooter if you put a request in the plumber wanted section more people will see it and they will pm you direct

 

[davidingram]

I have a similar problem. Pressure drops to zero every night when boiler has not been running.
I've had a heating engineer visit twice, changed pressure relief valves, changes expansion vessel, changed automatic air bleed valves, etc. There are no visible signs of water anywhere.
The tundish WAS dripping, but now we replaced the pressure relief valves it is not.
We bleed air from the system after each filling.
We have an Osma underfloor heating system over wood floors downstairs, rads and heated towel rails upstairs.
Outside we have a Grant Series 90-120 oil fired boiler.
Its driving me mad, I'm at a total loss...
Anyone have any suggestions of how I can systematically locate the problem, like a step by step guide?

 

[stevetheplumber]

I have a similar problem. Pressure drops to zero every night when boiler has not been running.
I've had a heating engineer visit twice, changed pressure relief valves, changes expansion vessel, changed automatic air bleed valves, etc. There are no visible signs of water anywhere.
The tundish WAS dripping, but now we replaced the pressure relief valves it is not.
We bleed air from the system after each filling.
We have an Osma underfloor heating system over wood floors downstairs, rads and heated towel rails upstairs.
Outside we have a Grant Series 90-120 oil fired boiler.
Its driving me mad, I'm at a total loss...
Anyone have any suggestions of how I can systematically locate the problem, like a step by step guide?

basicly you need to section the pipework and preasure test