Losing pressure in Central Heating system - going crazy!

cheme7676

km1500 said:

not sure if this is a stupid question or not but on the basis any idea might help... - have you tried a turning the central heating pump on but with the boiler not firing. 

(I can do this on my system by turning the thermostat up but the boiler water temperature off)

ie is it an increase in water pressure through the radiators because of the pump that is causing a possible leak or is it a temperature thing that's causing a leak

Well when I left my boiler cold for a few days at 2.0 bar (which is what my pressure gets up to when CH is on), I didn’t get any pressure loss. So I would think the result would be similar in this case? Possibly or not.

I was thinking of isolating the CH system and just letting DHW flow, with the idea of proving whether or not main HX is at fault. If I can rule out HX 100% then it might be worth me bringing in specialists

cheme7676

Okay so ignoring the radiator I spoke about for a sec, as I believe it might actually be due to the rubber feet it sits on which is attached to the metal support on the wall. Because when I tried to push the radiator slightly, it gave me a very similar sound. It may not be water at all but we can come to that later in my opinion.

Flue still not showing any smell, but it might be possible that it wont, because it might be that the extreme heat conditions burn it off? It’s more volatile than water so it’s possible I wont smell it in the condensate either.

i think that leaves us with two options that I can think of. Either I put something in the system such as a dye, or I can try isolate CH and just keep hot water going and see if we observe any leaks

FreeBear

cheme7676 said: i think that leaves us with two options that I can think of. Either I put something in the system such as a dye, or I can try isolate CH and just keep hot water going and see if we observe any leaks

Something like the perhaps - https://www.thesafetysupplycompany.co.uk/p/9385415/uv-condensate-drain-dye-identify-the-cause-of-leaks-and-faults-food-safe-gc-dtd250.html

A typical domestic central heating will contain somewhere in the region of 50l to 100l of water. So if you use one of these dyes, watch the dilution rates.

ThisIsWeird

cheme7676 said:

Just put some perfume in and waiting. Been around 20 mins but no smell out of condensate or anything yet.

i noticed the condensate trap was pretty dirty and very misty again (like a dark grey) even though a week ago it was cleaned. Not sure if that indicates anything…

Will wait in the meantime

I'm guessing just combustion debris.

ThisIsWeird

cheme7676 said:

The radiator is on the bottom floor and I can’t see any signs of water damage on the wall or skirting. Flooring is tiles and it’s an outside wall. Very small sprinkle of rain outside.

Are the pipes in the wall, coming from above, or under this tiled floor?

Regardless, an expansion ticking sound can be very like drips.

Also, I'd expect the drip rate to drop as the system cools down, from what you know about when your pressure loss occurs. I suspect, a ticking on expansion, and then - with CH turned off - a ditto with contraction.

I've been running our wood stove over the past few days, and it ticks like a Swiss watch when heating up - it just goes on and on, and I can't believe it's down to the tiny amount of expansion taking place. Then I open the door to add a log - and it immediately begins ticking rapidly again, I assume from it being cooled by the door being open. It's astonishing how quickly it reacts, and also goes on for. 

ThisIsWeird

cheme7676 said:

I was thinking of isolating the CH system and just letting DHW flow, with the idea of proving whether or not main HX is at fault. If I can rule out HX 100% then it might be worth me bringing in specialists

I think it's time.

Drop the whole system pressure down to no more than one bar - it'll still run, and that should give it plenty of expansion room.

Chuck everyone into the shower...

ThisIsWeird

How did you add the 'fume? 

And, if you bleed a teaspoonful from a rad, is the smell noticeable?

cheme7676

Excellent, will use dye and UV torch as last resort if we can’t confirm through this test.

So I took CH off at 16:30 and left DHW on, but I did NOT isolate the boiler yet with valves. I’ll leave all the pipework etc cool down, and for the pressure to settle for around 6 hours (11ish pm) then bleed/topup to 1 bar exactly. I don’t any contraction of the metalwork to give me a false indicator of a leak.

I poured around 100ml into a rad, closed up. After a couple hours I bled another rad on the ground floor and it came out strong smelling. However the rads on the 2 floors above did not show that much of a smell when I bled. I could just about get a small whiff of what I added though. Mostly a metallic smell is the way I can describe it?

Also, I want to add something else to provide you all with some more information which may (or may not be helpful). That valve with green deposits, I’ve cleaned and isolated the respective radiator. That radiator is the middle floor bathroom which has no windows and the radiator historically suffers from external corrosion (with no leaks witnessed). I usually treat with kurust and repaint with enamel. The radiator paint I applied seems to be “bubbling” and some parts flaking. Once again it brings us back to the question, with the quantity of water I’m losing, surely it would show even when that rad is super hot? This one is for you guys with most experience 

ThisIsWeird

This just cannot be the odd drip or seep, but a steady dripping when the pressure drop is occuring. 
A 2 to 1 bar pressure drop must surely represent at least a cupful of water, or more?
It'll either be very obvious when you do find it - a sizeable damp patch, stained surroundings, that sort of stuff - or else it's being lost via a hidden route!
I cannot see this rate of loss being 'disappeared' by evaporation.

cheme7676

Right, we have a development.

So the way I was testing the flue was using a plastic cup and tissue paper inside (in hopes for the smell to cling to the tissue). Then after a few hours of firing id place the cup over the flue for a few seconds and release. Did this about 10 times over 2 hours however I couldn’t smell anything each time.

i just got back to the house and brought some food colouring to also put into the radiators, i decided to smell the cup again and I can nearly definitely smell a whiff of the perfume I put in. Although it’s not overwhelming, I’m pretty sure it’s there. But I think we should just double check.

so with the above, we currently expect a cracked HX. So in theory, using the water should result in a degrade of pressure with hot water isolated. 

Assuming that it will, I will add some of the dye I bought (green, as opposed to red/yellow/orange to not confuse with rust) into a radiator now in preparation that we expect to see it in the condensate once we relaunch Central Heating tomorrow/Monday? Hopefully by putting it in now, it might have a bit of time to naturally diffuse somewhat through the circuit, so that we save a bit of time