HELP... Combi boiler heater pressure?!....

[__james_]

Hi there!


recently my Valliant combi heater (VCW 20/1 T3 WH) decided not to work... http://www.howtomendit.com/answers.php?id=51340


today i replaced the circuit board and it works!


however... reading the valliant manual it seams the boiler pressure when cold should be just under 1bar. so i topped up the system (it was at about 0.4 bar i think!)

turned the central heating on and watched the pressure gauge... it rose in a few minutes as the water/boiler got hotter. it rose just past 2 bar and i got scared so i turned it off... the gauge goes to 4bar but there is a red line at 2.5 bar (hence why i turned it off!) but i know in the manual it says if it goes above 3bar then a pressure release valve opens.


anyway, getting to the point... what pressure should my boiler be at when cold and when in use?!

am i right in thinking it should be just under 1bar when off and about 1.5bar when in use?!


thanks for your help and time!


James

ps. i have searched the net all night for this pressure question answer but no luck, but i did find this forum, which i have also searched for the answer but no luck, hence this thread!

 

[bster]

As long as the pressure relief pipework exits the property and terminates safely and the PRV is rated at 3bar (ie hasnt been replaced) let the boiler run, if it the PRV opens then you have a problem with your expansion vessel. You will probably (hopefully ) find that it will stay at 2.5bar.

 

[kevplumb]

am i right in thinking it should be just under 1bar when off and about 1.5bar when in use?!

depends on the amount on water in the system

 

[__james_]

thanks for the replies guys...


at the mo im running a bath as a test with the central heating off to see what the pressure gauge does!...

the bath is half full and the pressure is fine! (hasnt moved!)


so what you two think i should do it try the central heating again and see what the pressure goes to?! hopefully it wont go higher than 2.5 bar which you think is normal?!


correct yea?!


if it does go over 2.5 bar should i turn it off before it reaches 3 bar, as the last thing i want to do is damage the pump or anything else!


thanks again for your help!

 

[kevplumb]

the bloody ex vessel needs pumping up

have a look in FAQ at the top

 

[libby lou lou]

F A Q ?

 

[Agile]

With a typical three bed semi ( or even a two bed flat ! ) the pressure should be set to about 1.2 bar cold and rise to about 1.5 bar when the CH is hot.

If it goes above about 1.8 Bar then the expansion vessel needs recharging or has failed. See FAQ section for some ideas on how to recharge. It must be done properly.

Your boiler is now about 20 years old and many of the expansion vessels have failed or will do shortly.

Whilst its solidly made you should start thinking of replacing it if only to benefit from the increased efficiency of a condensing boiler.

Tony Glazier

 

[__james_]

F A Q ?

frequently asked questions!


//www.diynot.com/forums/viewtopic.php?t=37170

 

[__james_]

With a typical three bed semi the pressure should be set to about 1.2 bar cold and rise to about 1.5 bar when the CH is hot.

If it goes above about 1.8 Bar then the expansion vessel needs recharging or has failed. See FAQ section for some ideas on how to recharge. It must be done properly.

Your boiler is now about 20 years old and many of the expansion vessels have failed or will do shortly.

Whilst its solidly made you should start thinking of replacing it if only to benefit from the increased efficiency of a condensing boiler.

Tony Glazier

thanks for the reply...

as it goes its a 2 bed ground floor flat i live in and not a typical three bed semi. the block of flats is 3 stories high and the flues all go to the roof and i am thinking that possibly that any pressure release valve would be higher up?! would this therefore make any difference to your anticipated readings/advice?!

thanks again!

 

[__james_]

just did a quick test... i turned the CH back on and within about 10 mins, after all the rads had got hot the pressure had rose from 1bar to 2.8 bar and was rising still!

again i got scared and turned the CH off


does this confirm that the expansion vessel needs pumping up/recharging as kevplumb/Agile has suggested?!

am i best to get someone do this for me and service the boiler at the same time?! (it hasn't been serviced for a few years!)



thanks again ppl!

 

[__james_]

bump....


anyone have an answer the the above post?!

 

[__james_]

ok so i called the local pluming shop that i got the new circuit board from...


told them about the pressure situation and the guy said to me to turn the CH on and see what happens. he said if it does go over 3 bar then the PRV will come into operation and the boiler will more than likely turn its self off!

he said that his boiler rises to 2.6 bar when hot.


so anyway i turned the CH on and the pressure rose to 2.85 bar and the rads were all hot, the boiler then turned itself off (as it had got to temp i guess!) and the pressure dropped to 1.6 bar and then the boiler/fire came back on and the pressure rose to 2.4bar and then the boiler would turn off and the pressure would drop again to 1.6 bar and this cycle would continue!


now what i want to know, is this normal for my valliant combi heater?

or do you think the pressure is still too high and that the expansion vessel need pumping up/recharging?!

 

[JohnD]

Q. When told by experts (not shop assistants ) that your expansion vessel needs charging or replacing, why don't you believe them?

Also: If the pressure builds up and the escape valve opens, it will probably not seal tightly again, and will drip until you get a new one fitted. This might be why the pressure was low.

 

[__james_]

Q. When told by experts (not shop assistants ) that your expansion vessel needs charging or replacing, why don't you believe them?

Also: If the pressure builds up and the escape valve opens, it will probably not seal tightly again, and will drip until you get a new one fitted. This might be why the pressure was low.

A. because i have been told different things by different "experts"!

I have had an engineer round and he was not sure of the problem! (he guessed circuit board).... the "shop assistant" as you put it (tho how u know he isn't an "expert" i don't know?! ) suggested to me it was also the circuit board... it seams they were both right!

though now i have a different problem!


i do appreciate the help of people on here... but because i have been told different things by different people i am trying to get as much advice as possible (any advice is good advice!) before i go out and spend more money!


so back to the topic... your opinion is that the expansion vessel needs charging or replacing?!


Also i have noticed/forgot to say... last night i topped up the pressure via the filling loop so the pressure was at 1bar when cold.

this morning the pressure had dropped to 0.7 bar and its now at 0.3 bar!

so do i now have a leak?! it hasn't been over 3bar so it cant be the PRV?! and i have checked the filling loop isn't leaking or the rads!


so does this sudden lose in pressure again indicate the expansion vessel needs charging or replacing?!


thanks again!

 

[JohnD]

You may have had PCB-related problem earlier, but I am thinking about your current problem; the pressure was too low and goes too high when hot after you've refilled it.

Pressure problem... surely not PCB related... Agile and Kev had done more of these than I've hot babes... makes sense to me

p.s. I'm guessing that if the guy behind the counter was good at mending boilers, he'd be out there doing it. But I suppose he might be taking a break.