Pressure loss

joeirish · 03-04-2020 5:14pm #1

Hello, I have a loss of pressure in my system. But not all the time. I've been checking it and it drops from the normal 1.3 to nearly zero over a few hours when the washing machine or dishwasher is running. It doesn't seem to drop when the CH goes on or off and has maintained the pressure most of today since it dropped this morning while the washing machine was running. This has been going on for a few weeks now but I have been trying to find the cause. I can't find any leaks anywhere. Any ideas? (Unfortunately the plumber who installed the system is in Germany where he is quarantined because of catching Covid-19 so can't help). Thanks in advance.

John.G · 05-04-2020 9:26am

Hi Joe, presume you mean your heating system....have you got gas/oil boiler?.
Also check for a filling loop with a pressure reducing valve (PRV) and a pressure gauge, you may find that your expansion vessel is full of water or after loosing its pre charge (air) pressure. The PRV may be set up in "auto fill" mode where the mains is left fully open and the PRV will maintain 1.5 bar irrespective of any system leaks. Also if the E.vessel is faulty then the boiler "safety" valve (also called a PRV) will lift when the system contents heat up and dump all the expanded water out its vent and if the filling pressure is too low due to washing machine/D.washer use then it cannot refill the system.
Its easy to check if the safety valve is lifting, you will see a little pipe coming out of the wall (if a gas boiler), just tape or tie wrap a small plastc bag around this and check later for rupture or water in the bag, an oil boiler will generally have this fitted on top of the boiler or very close to it, on the flow pipework.
It could of course also be a system leak.

joeirish · 05-04-2020 9:51am

Thanks for the help. Here's the thing. It seems to be OK now. So I'm trying to figure out what I have done over the past couple of days. The main thing is that on the heating circuit (we have ufh on the ground floor) the plumber has also connect a towel rail upstairs. Now there is a motorised valve but for some reason that has never been connected to the controller. So when the ufh is on the towel rail warms the upstairs bathroom. It is controlled by a thermostatic valve. I turned this down the other day and since then the situation seems to have resolved. So I'm going to turn it up again and see if this is what is causing the problem. I'll let you know and maybe ask what I should do next if this is the issue.

John.G · 05-04-2020 10:00am

Before you do (or after) check that the pressure is changing as the system heats up, if cold pressure is 1.5 bar....expect to see 2.0/2.2 bar when hot. Towel rail may be full of air, can you vent it.

joeirish · 05-04-2020 10:06am

I have been keeping an eye on it and it is pretty constant, not moving up or down regardless of any heating or cooling. Attached photo of the pressure guage. I've been using the red tap on the left to introduce more cold water into the system when the pressure dropped.

John.G · 05-04-2020 10:20am

I'm surprised that there is no movement in the pressure gauge, it can't be the gauge itself since its dropping to zero, its also thermodynamically impossible that it doesn.t rise/fall with system temperature changes if no leaks. Its a nice neat install, I see there is a PRV (safety valve) fitted here (with red top) but there should or probably is one fitted at the boiler as well, have a look and post a pic. Also, if the boiler is new say a Grant/Firebird then they will have their own internal E.vessel, if not you should see a red one somewhere around.

joeirish · 05-04-2020 10:31am

Hi

The boiler is about 5 years old. Its a Grant Vortex Condensing boiler in an outside housing. Pic of the top attached. I think the yoke on the left is the pressure valve. Not seen a pressure vessel and I can't find mention of one in the user manual. In there is shows positions for expansion vessels and I think that is what my plumber did. You can just see it in the earlier photo I sent above the pressure guage.

joeirish · 05-04-2020 10:40am

Actually just went and had another look at the thermal store and there is another pressure guage. Photo attached. You can see it in the middle of the photo near the back. I haven't been watching that one and maybe it is that that changes as the water warms up. I'll keep an eye on it today.

John.G · 05-04-2020 10:42am

I saw that but thought it was for a unvented hot water cylinder as the CH E.vessel is usually red, hope there is no tie in between your two systems (very unlikely). Have you got a unvented hot water cylinder?, also at one end of that white E.vessel you will see a plastic cover, just unscrew/prise this off and you will see a schrader (tyre type) valve, press this with your finger nail and ensure air comes out.

Just saw your new post and will revert.

joeirish · 05-04-2020 10:49am

HI, I've just got the one unvented thermal store. It's a german design and fairly complicated. Basically the 500 litres hold the heat and coils inside take in cold water for dhw and heat this so there is a constant flow of hot water out of that coil. A second coil is for the UFH. A third coil is used to heat the thermal store with hot water from the boiler. (I also have PV panels supply elect. to the immersion when the house is not using the elect. produced.) Attached diagram of the thermal store.

joeirish · 05-04-2020 10:52am

Yes, air comes out when I press the valve on the pressure vessel.

John.G · 05-04-2020 11:14am

If the ufh is separated from the boiler coil then the ufh must have its own E,vessel and the boiler system must have its own E.vessel, so is that top up valve that you are opening/closing supplying water to that white E.vessel or what? also in pic. gauge.jpg, it shows another flexible filling? line, can you see where that goes?
Its a bit complicated alright but as you say just watch the second pressure gauge for rise/fall and at least it will probably identify that as the boiler system, also of course, the thermal store pressure gauge should rise/fall as well, but maybe not a lot if the thermal store temperature is fairly constant. Anyway watch that second gauge for rise/fall and post back.

joeirish · 05-04-2020 11:26am

The ufh and the boiler are connected. It's the way the plumber installed the system. Basically there is a flow and return from the boiler to the thermal store. Off of these are two spurs to the flow and return to the ufh manifold. So the same pipes that connect the boiler and thermal store are also the same pipes that connect the manifold to the thermal store. So when the ufh pumb comes on at the start of a heating cycle it cause the pump to fire up. If the water in the thermal store is hot enough the pump turns off after a few seconds and heat for the ufh is drawn from the thermal store. Each time a thermostat asks for heat the pump turns on (or increases speed to be precise). This in turn causes the boiler to fire up for a few seconds then it goes off again and heat is once more drawn from the thermal store. If the thermal store is not hot enough the boiler keeps on until the temp is high enough in the thermal store. There is a separate coil for the DHW which draws heat from the thermal store. The boiler comes on if the thermal store is below a cut off temperature (around 40 degrees I think).

joeirish · 05-04-2020 11:31am

I just found a photo showing the thermal store. The two lagged pipes coming from the floor to the top of the TS are the flow and return from the boiler. If you look carefully you can just make out one of the spurs that connects to the manifold for the ufh. The other is hidden behind the ufh pump.

John.G · 05-04-2020 11:40am

It makes sense that the UFH & the boiler system are as "one" so where is the E.vessel?
Also the pressure gauge that's falling to zero, is this on the filling loop for the thermal store E.vessel (white one?)

joeirish · 05-04-2020 11:58am

The only e.vessel is the white one so I guess that is for the UFH.

Attached is another photo of the two guages with each labelled this time. Pressure guage 1 is the one that moves when I open the filling valve and this is also the one that was showing the pressure dropping. However the filling loop (with the red valve on it and the coiled pipe) actually has Pressure guage 2 on it. And this does not move when I open the filling loop valve. That is also the pressure guage that is on the filling loop to the e.vessel.

John.G · 05-04-2020 12:26pm

I will have to sit back and think, I wonder is there any chance that the boiler is connected directly to the TS, ie no coil and that the solar input (which has its own EV) is from a coil and as you say the hot water is from another coil.
I'm also confused re PG1, as you say that the filling loop goes to the white EV (and PG2) can you see exactly where that "PG1 pipe array" goes, remove the bit of lagging below it and see if it goes directly into the TS or/and elsewhere.

What confuses be most is that the filling loop goes to PG2 via a PRV but has no effect on this gauge but does increase PG1 pressure even though its not connected to it, maybe one filling loop serves both (with their own PRVs (pressure reducing valves) the TS EV and the boiler/UFH loop EV?. Maybe take a few more pics around those PGs and the top of the TS, should be able to figure out what what.

joeirish · 05-04-2020 12:56pm

Attached are some more photos, labelled where I can. latento2.jpeg

latento3.jpeg

joeirish · 05-04-2020 1:00pm

Also a diagram from the TS manual showing the various connections on the top of the TS. Now as we don't have any solar panels (water heating version) the plumber has used the solar feed and solar return as the flow and return from the boiler. Hope this makes sense, I'm trying to remember what he told me at the time.

joeirish · 05-04-2020 1:02pm

And one final view of the top of the TS

joeirish · 05-04-2020 1:05pm

Photo showing pressure vessel.

John.G · 05-04-2020 1:32pm

Just give the base (but not the gauge/glass) of PG2 a few judicious taps of the handle of a adjustable spanner or whatever to ensure the gauge isn't sticking, after a quick look at your pics (will have a better look a little later) its hard to explain the non movement of PG2 when PG1 does move??

Also give a few details of the EV...capacity etc.

Re solar coil: it is common practice in a conventional twin coil HWC to connect in BOTH coils where the solar isn't installed or is awaitng installation.

joeirish · 05-04-2020 5:30pm

EV is 35 litres.

Looks like PG2 is going up, it wasn't moving before because the TS temp was constant. I changed a setting to allow the TS to get a bit hotter, and manually turned on the DHW heating cycle. But we're only talking about 5 degrees increase in temp so not sure if this is enough to effect the guage.

John.G · 05-04-2020 5:48pm

Hi Joe, think I can see now at least how it is connected in. (look at pic tank top3 & latent tank top diag1, attached) The two coils do seem to be connected in series, the cold boiler feed comes in on the second connection from the right in the the row of 5 connections in the middle of the TS, marked "Heating circuit return removal cold" flows through this coil and exits at the second connection from the left marked "Heating circuit Feed discharge Warm" and via the elbow plumbed in, enters (third connection from left) the solar coil marked "solar coil warm" flows through this and exits at the connection at the rear top right of the TS marked "Solar return Cold" and back to the boiler. The EV is teed into this so IF my interpretation of the set up is correct then both PG1 and PG2 should read the same so a bit of a mystery here for the moment, anyway have a look at this and see if you agree and we can take it from there.

Edit: just saw your post now so we are really left with two riddles, why is PG1 going to zero and where is the EV for the TS? which should be 50 or 60 litres IMO.

Also what drew your attention to PG1 originally??.

Also where are the connections for the hot water coil??.

joeirish · 05-04-2020 6:08pm

So just checked and both pressure guages are more or less the same, between 1.1 and 1.2 so allowing for the fact that are different makes would this constitute reading the same as you expected?

You say "the cold boiler feed comes in on the second connection from the right". Not sure if that is correct. The pipe coming from the boiler is at the moment extremely hot so not a cold feed but a hot feed. And this is the one that also feed hot water to the ufh manifold and into the second connector (labelled Heating circuit return removal cold on the diagram).

The EV is teed into the other pipe to the boiler, the colder one of the two and I assume this is the return?

I've attached another diagram showing the coils in the Latento TS. Not sure if this will just cause more confusion or clear things a bit!

John.G · 05-04-2020 6:21pm

Yes of course, "cold boiler feed" should have read "hot boiler feed"

I wonder why was PG1 reading zero at times though even if same as PG2 now.

Where are the domestic hot water connections and are we missing a EV somewhere.

Did a quick calculation, a 35 litre EV would be adequate for a 500 litre TS but this white EV is plumbed in to the primary (boiler) heating circuit.

joeirish · 05-04-2020 6:31pm

OK. By the way here is the hydraulic diagram that I believe my plumber followed.

Now not sure if the two PGs were reading different, I think PG2 was always on around 1.2 whereas it was PG1 that dropped and I used the feed loop to raise the pressure again.

And I may have not fully properly labelled the hot and cold pipes on the left of the photo latento2.jpeg. Where I said Hot and cold to bathroom and shower, these also extend downwards and behind the TS but I think they are the H&C for the downstairs DHW.

joeirish · 05-04-2020 6:33pm

So only one EV on the system. And here is the other photo showing the DHW pipes I mentioned in the last post.

John.G · 05-04-2020 6:43pm

Probably getting a bit tired now but is it designed so that one EV can serve both requirements??, As I said above I can see quite clearly how it services the primary circuit but how is it connected to the TS?.

joeirish · 05-04-2020 6:51pm

Thanks a million for your help. On the connecting to the TS, I don't think it is except into the circuit/coil that runs through the TS. The actual water in the TS is not under any pressure it is just the coils that hold the ufh fluid and DHW that would be as far as I can ascertain. I'll be messing with the system during the week and checking if I can replicate the issue of dropping pressure. Perhaps it is just a faulty TMV on the towel rail 'cos when I turned that down the issue seemed to resolve itself. I'll post on here when I have it sorted and thanks again.

BTW where are you based and are you stuck at home unable to get out to work.

Cheers

John.G · 05-04-2020 7:10pm

Very good, so a vented TS.

Not at work Joe because I'm far too old but I had a good run for 47 years or more.

Pressure loss

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