Is 3 bar too high for a combi oil boiler?

[quartzz]

Just as the question really....

There is some history but the boiler fairly regularly loses pressure, and I have to turn a blue wras lever (that I'm told a previous plumber apparently installed) to get pressure back up (every 2 or 3 days, almost always in the morning after overnight). when I re-pressurise, the boiler normally kicks in at about 2.5 bar

I think I over bled one of the downstairs radiators (to try and fix what turned out to be a stuck TRV pin valve) so the whole system is "missing" about 50mL of water, whether or not this is relevant

just to edit with information in the rest of this thread. so the system isn't "missing" 50mL, because any time I re-pressurise the system (blue lever), that re fills it with mains water pressure. I'm keeping an eye on the pressure while it's all working, rather than just moving the lever when it doesn't. It's humming along at 2.6 at the moment

 

[Madrab]

3 bar is when the the pressure Release Valve in the boiler lifts and lets the pressure out of the boiler, its one of the main safety devices in any sealed boiler system, so yes 3 bar is too high. That high a pressure for extended periods of time will also put stress on the expansion vessel and other connections/seals

A sealed boiler will look for around 1 bar before it clicks on, if it's not doing it till 2.5bar then there is something wrong with either the gauge or the pressure sensor.

Sounds like your system needs to be looked at and the leak found if it's every 2-3 days!!

 

[quartzz]

thanks I'm sure this is a very in depth subject, but what actually causes the pressure to increase to that 3 bar level? if there is a leak somewhere would that not cause it to lose pressure rather than build up? by the way could relatively low oil level in the oil storage tank cause this?

I'm also actually wondering, I moved into this property in Oct 2024, I could have sworn that the first time I had to move the blue wras lever, it did actually kick in at just over 1 bar, and that the "kick in" level has gone up since then

 

[trojanhawrs]

You're letting water from the cold main into the heating system, so whatever pressure you get off the main is what you'd be able to charge the pressure to. Even if you have 3 bar mains pressure though you only want to charge to between 1 and 1.5 bar.

 

[quartzz]

thanks so the central heating is a closed system, am I right in saying that? if I took one of the valves off the towel heater in the top bathroom (top of the radiator) and poured water in from a jug, would that "fill in" any air gaps? but that would just fill it to 1 bar I would guess?

 

[quartzz]

edit - I did have a text message (and voice) dialogue with the heating guy who installed the wras lever, I told him the current pressure (this was about 2 months ago) was 2.8, he said that's fine (quote). two months ago according to the text I sent, it was about 2.3 bar. 10 minutes ago is actually the first time I have checked the gauge while the boiler has been actively heating the house. I'll check it a few more times over the next few hours

 

[trojanhawrs]

As soon as you open a valve it's no longer a closed system. If you open a valve at the top of the system it'll push water out until the pressure is equalised e.g. 0 bar.

 

[quartzz]

This is what (confuses/curious/need more input [short circuit film reference]) question is I'm trying to understand....if I accidentally let out about 50mL of water from over bleeding, does that mean the closed system now is missing 50mL of water, and when I re pressurize the boiler, does that pressure go back into the main central heating system, or is the boiler re-pressure a seperate "circuit"? (when I open up the blue wras lever to hit 2 bar or so for it to kick in, it sounds like air is being pressured back in -- but is it actually water being pressured in, and does that pressured water refill the 50mL I accidentally bled out?)

If I do open up this valve at the "top" of the system on the towel rail, will it have spare space to put the water in that came out during the over-bleed, or will water actually squirt out the top? appreciate the info.... again if this is "confidential" information that will take money out of someones next job I can understand...

 

[trojanhawrs]

It's the same circuit and yes it's water. Yes, you're letting 50ml of water out but there is also an expansion vessel on the circuit, these are normally built into the boiler (but external ones may also be needed for larger systems). This is a tank charged with air with a bladder inside to keep the water separated from the air. The purpose is to allow the water to expand when it heats up without raising the system pressure to extreme levels that could burst the pipework (it expands into the bladder and compresses the air in the tank). So if you charged to 2 bar and bled down to 1.2 for example, it doesn't mean you're missing water (unfortunately its no guarantee that there's no air in the system either)

 

[quartzz]

thanks I've seen the expansion vessel yes, largish round grey disc, about the diameter of a football. I saw it from taking the boiler side panel off then a few googles later found descriptions of what I was looking at

ok cool so I think I'm learning something. the 50mL let out from the un necessary bleed, gets replaced by (what sounds like) an air scoosh when I re pressurise? so that re pressurise isn't anything "mysterious" to do with the boiler or injecting air, it is actually putting water back into the main central heating pipework? (tell me if I'm getting any of this wrong!)

so...if that is the case....the question is....the main central heating pipework system is apparently leaking water, for me to have to re pressurise it 2-3 times per week.....? so if I did open up the towel rail valve, would I expect that pressure dial to move to "1" as I opened it? (I couldn't view it actually happening because the boiler is outside and the towel rail is in the bathroom?)

and there will definitely be a boiler call out some soon I think....just trying to get a handle on what the system is doing

 

[quartzz]

so if possible if you or anyone could tell me if I've got this right. I thought that this pressure dial (3 bar) was air, and was some mysterious subsystem inside the boiler. but the 3 bar is actually the water pressure of the entire central heating pipework inside the house? so if I did open a valve, 3 bars worth of water would sort of squirt out from the valve until the dial read 0 bar (atmosphere)?

ok yeah from the online manual

"When the boiler is connected to a sealed system the
system pressure should be periodically checked. The
minimum pressure, as indicated by the black needle,
is 0.5 bar when the boiler is cold and 2.5 bar when
the boiler is at normal operating temperature. If the
pressure is outside this range contact Warmflow or
your installer."

so the 2.8 it was at before, the guy shouldn't really have said it was fine......although he may possibly know more than me. the boiler was essentially switched off for 3 weeks before I moved in, so that might have done something. and also right now my oil in the tank is very low (about 10%), due to have 500L in a couple of days

boiler has been off for an hour or so and it's sitting there silently at about 2.2 bar. I'll keep an eye on it now I know more about what I'm looking at, and it didn't occur to me to check it while it was all powered on

 

[Johntheo5]

Oil fired combis hold around 40L of primary water in the heat exchanger and primary store so the EV is normally larger than one for a system boiler only. I think the 36kW Grant (combi) has a 14L EV, if precharged to 0.7bar and filled to 1.3bar (COLD) then a total system vol of 140L will result in a final pressure of 1.95bar (Hot), precharge/filling pressures of 1.0/1.5bar results in a final pressure of 2.13bar (Hot), and precharge/filling pressures of 1.0/2.0bar results in a final pressure of 2.96bar (Hot), which on a Grant will lift the PRV because its set to 2.5bar, no boiler should have a filling pressure of 2.0bar, 1.5bar max, the above pressures assume rads etc vol of max 100L. + 40L boiler vol = total system vol of 140L. Most other oil fired combis have a 3.0bar PRV.

Would suggest next time the system is pressurised, press the EV schrader valve pin, if water comes out for more than a few seconds, then new EV required, if only air, EV OK, depressurise systam completely, remove the connecting pipe from the EV, pump up/ensure the air end at 0.7bar, reconnect pipe, fill the system to a max of 1.3 bar (all COLD), see how you get on.

What make/model/power output combi do you have??, how many rads, doubles/singles??, take off the side panel again, there should be a label on the EV stating its volume, note it.

 

[quartzz]

thanks but most of that is a foreign language to me (I'll have to re read it) and also sounds more technical and involved than I should be attempting. it's a warmflow KC90HE (installed 2017 as far as I know), has been serviced regularly (most recently last June or so I believe), but the boiler servicer (to my knowledge) installed this wras blue lever because of the losing pressure thing (previous tennants were in the property before me, they had the boiler servicing done). I've just checked the pressure this morning before turning the heating on, and it was 2 - central heating fired up no issues when I changed the thermostat. currently running at 2.6

One question I could ask......usually I have the hot water switched off to save money, would it be wise keeping the hot water "on"? I kept the hot water "on" last night to see if that would help in it not losing pressure (in my mind, to keep the boiler "ticking over" overnight)

Also....is it better to have the central heating "off" on the wall timer control (Drayton control panel), or to have it permanently "on", but to turn the thermostat down manually when I don't want heat? (or.....doesn't it matter)

The whole system is 5 TRV + 1 towel rail heater (2x TRV downstairs - both have been in use over the winter, 3x TRV upstairs (1 has been in use, the other 2 mostly turned off). I moved into this property Oct 2024,the kitchen radiator downstairs wasn't heating up when I moved in, I tried a bleed which didn't work, kitchen turned out to be a stuck TRV pin, which is still stuck).

 

[Johntheo5]

That boiler has a 12L EV which is more than adequate for the number of rads you have. As stated above, the boiler should refire when the pressure, at most, is 1.0bar, if the pressure is say 2.5bar when it shuts down at night then it should still be 1.5bar in the morning when cold, keeping it hot overnight will do nothing for it if there is a leak, you need to get someone in who knows what they are doing.

 

[quartzz]

I'll need to start doing some checks that I hadn't done before. when it was working I hadn't paid much attention to it. I'll need to start doing some checks when it's "good". some parts of the manual contained information which was completely alien to me without some introductory knowledge -- which I might be more familiar with now

but yes, when the boiler servicer arrives, I'd prefer to be able to tell him some basic numbers rather than just "sometimes I have to press this blue lever"