Pressure escaping from heatslave boiler. but where?

[fleetfox]

I have a heat slave 15/19 oil fired combi boiler that is driving me and my plumber up the wall. It was losing pressure over the course of a couple of hours until it only held about 0.3 bar.

Plumber came out, couldnt find any leaks anywhere (walls and floors dry, valves etc around all rads dry, house generally dry) so focused attention on the boiler. Decided as the overflow was a damp along with the ground outisde that the PRV had gone. took it off an it was knackered so replaced it. Went away and started boiler as normal.

Came down the next morning with pressure at 4 bar! released pressure but slowly pressure would creep upwards whether boiler on or not. disconected filler hose just in case the valve was knackered but still rising slowly. Plumber called Worcester Bosch who decided it must be the heat exchanger. Got a new one fitted.

Woohoo! Pressure not rising, but now pressure is back to falling gradually over the course of a couple of hours. It seems to fall more quickly when the heating and water are OFF! i wonder if this is because the system cools and contracts and reopens any fault. I am really stuck, there is no sign of any water anywhere. What could be causing my slow pressure release? PLumber is at a loss!

HELP!

 

[cider]

Presume you checked the expansion vessel

 

[Burnerman]

.....and the automatic air vent on the boiler top - another notorious part for failure.
John

 

[fleetfox]

Hi both and cheers for the response.

Have checked both and they appear fine. I suppose my question is looking at what you have said is as follows: Can air escaping be causing the pressure loss in the system? Since i am topping the water up a few times a day through the filling loop (to get it back from around 0.3 up to around 1.2 bar) i had assumed that it must be water escaping from somewhere. Now you have sent your post burnerman i wonder if there is anywhere that air could be coming out (i thought since it was a sealed system there shouldnt be any air in it.

One last bit of info i discovered. The boiler doesnt lose any pressure whilst running. Have had it on for four hours now and running nicely at around 1.2 bar. However when i turn it off it loses all its presure over about 2 hours.

If you could magically come up witha solution it could save me a couple of grand. (the boiler is only four years old for goodness sake)

thanks!

 

[Burnerman]

There is such a limited amount of air in a sealed system (i.e in the expansion vessel) that even if this was full of water due to diaphragm failure the pressure would stabilise, and any excess pressure would shoot out of the PRV.... check the EV pressure anyway to around 10 psi. (System depressurised).
As the CH water pressure must be less than the mains, there's no way that it can be returning via a heat exchanger. Are you certain the new PRV is behaving?
John

 

[gblades]

Sounds similar to the fault I have with my ch system. It also did not seem to loose any pressure when the system was on but overnight it would drop from 1.1 down to about 0.3 bar.

I could not find any damp spots either so concluded that there must be a leak either in the pipe which runs around the kitchen and up in the box section in the wall or in one of the pipes to the downstairs radiators which run under the concrete floor.

I got a plumber in to drain the system and put gate valves in as the main 22mm pipe splits and goes to the manifold supplying the downstairs radiators. With this shut off I didnt loose any pressure. I have now been plumbing the downstairs rad back in via isolators to see which rad is the problem.

The reason why you are only loosing pressure when cold is probably due to pipe expansion pushing the pipe back into the faulty joint.

 

[fleetfox]

Thanks Burnerman, Ive had a pint glass under the escape pipe outside for the last two hours whilst the heating and water have been turned off. Pressure drop by around 0.4bar. Empty! so the new PRV seems to be happy enough. Since it has a brand new heat exchanger im pretty confident in that too.

gblades, this is my nightmare scenario. My house is 330 years old and most of the downstairs plumbing is under concrete floors, all the valves around the rads are bone dry on all floors of the house and the ceilngs and walls look fine (this has been going on for months so surely i would see something, i mean it is cold water after all!). Also regarding the floors my carpets are nice and dry, and there is no smell of damp.

I have read that you can put some anti leak fluid in the system, is this stuff any good? and if so would it solve the kind of problem i appear to have.

Finally it seems that you two also agree that there must be water coming out somewhere since i am topping up twice per day. The question now is how to find out where. Sounds like i dont need a new boiler after all. Again thanks to you both for the response.

Its going to be cold next week, this is driving me round the twist, its cost me £350 to get nowhere so far.

 

[gblades]

Thats an old house but the important thing is how old is the central heating system itself as it has to have been fitted after the house was built.
Concrete will eat through copper pipe so your pipework should either be encased in a plastic sheath, have a protector wrapped round it or be encased in a wooden box section.

In my house the 10mm pipework in covered in a plastic protector and comes out of the concrete under the kitchen sink and then goes to the manifold and the 22mm pipework is in a box section running round the kitchen and up into the wall.

If you can find where the pipe splits to go to the downstairs radiators you might be able to put isolators in there to isolate the system and then diagnose where the leak is.

Check where the pipes come out of the concrete aswell. Thats a common area where concrete can touch the copper pipe and eat through it.

I have heard of someone mentioning here in the past that some people can inject special gas into the pipes and then use a detector to see where it is coming up. A water leak under/in the concrete will just soak in and drip down and may not be visible from the top. A gas will rise up through if lighter than air and can be detected.

 

[gblades]

The anti leak stuff does work but for the severity of leak you have I dont think it will work.
Also with the leak being worse when cold I think its related to pipe expansion so any leak will just be broken apart again fairly quickly.

 

[fleetfox]

Hi there gblades and thanks for a really helpful post.

Here are a few further bits of context that you may be able to make suggestions for.

1. The boiler is a combi and is on the ground floor (under a chimney where there was once a range). The hot water used to be heated by the fire but this sytem although still in place is all disconected (from the fire) and not connected back up to the boiler.

2. The boiler was installed 4 years ago, it replaced a gas system that ran from bottles and looks to be plumbed into the old pipework that fed this.

3. The copper stems for each radiator on the ground floor (5 in total) pokes straight up out of the concrete floor (through and covering ranging from tiles, carpet and even cork).

Finally i cant tell for certain because there is boxing shortly after the hot water out pipe but im pretty sure it dives into the concrete only a few feet from the boiler itself, and from looking at it i cant see that there are any coverings on the pipes (i.e. all the stems poke up as just bare copper).

I have a horrible sinking feeling that im going to have to remortgage the house!!!!

 

[Burnerman]

Just a thought - before you pull the place to bits, pop the burner out to see if there is a leak in the water jacket....if there is, maybe the water has been escaping and then evaporating off.....probably way off beam though.
John

 

[fleetfox]

hi again burnerman,

The plumber pulled out the burner the other day and replaced the nozzle for me. Im hoping that he would have noticed if the water jacket was leaking. He seems fairly competent.

Ta

 

[gblades]

For that sort of pressure loss you are probably talking around 2-3 litres of water so would be a steady small stream of water. Wherever it is it is somewhere where the water can drain away without being noticed.

Always worth closely inspecting every that is visible or can be made visible fairly easily before looking elsewhere though.

 

[fleetfox]

Hi gblades,

re the amount of water thats what i was reckining per day ( a milk bottle or twos worth).

Also i have had the thought about where it could drain without me noticing. The only problem is that i just dont see how that much water daily could drain down through the concrete floor and away without me being able to tell. Surely the carpet would be wet or the tiles would unseat when i stood on them etc.

I will ring the plumber and get him to check that it is definitely the pipes. He says that he already knows this since the closed system has a pressure gauge and since this is falling the water must be coming out of the heating side of the system (i.e. rads or pipes).

As the heating system is situated at ground level is there a way he can isolate the ground floor section of the heating and check this alone for pressure loss just so that we are certain?

regards and thanks

 

[gblades]

When draining my system down (6 rads in total) its an easy 1/3 of a bucket of water that comes out for the pressure to drop from 1.1 to 0.3 bar but your system may well be different. If you have seen yours draining you will have a much better idea.

It depends where the pipework actually is within the concrete. I dont know how the concrete floors are constructed but if the pipe was at the bottom the water may not soak up through. Also the most likely place for a leak is in any join. A join will either be covered in a concreate proof protection similar to grase soaked cloth or encased in a wooden box to keep the concreate away from the exposed copper. This could help the water escape without getting in contact with the concrete.
I have had a leak before in my house and this was as the 10mm pipe went into the manifold. This was in the exposed pipework as it came out of the ground underneath the kitchen sink. I only thought this could be where the leak was because it seemed to be a bit humid under there and a lot of other pipework was there also so was a good starting point.

I doubt there are any isolators so cant really isolate the system. As I knew where the pipes ran I had a couple of gate valves put in to isolate the downstairs rads but thats something the plubmer will need to put in but the first step is to find where the pipe splits to go upstairs and round to the manifold supplying the downstairs rads. That would be where you would put the isolators and is also the most likely point of failure simply because its the are with the most joins in a single area.