what pressure for expansion vessel?

[hammer-time]

Hi folks,

Just wondering - what sort of pressure should be in the expansion tank vessel for a combi boiler?

It's an old worcester heatslave combi boiler, wall mounted, closed system, 11 radiators all on ground floor (bungalow).

I'll be draining the system before measuring the expansion vessel pressure - just wondering what ballpark it's pressure should be?

Talking of pressure - what sort of pressure should the system be filled up to when cold? Am I right in saying about 0.7bar?

I'm going to change the pump on this system because the thermal cutout in the combi keeps tripping. I assume a faulty pump sounds like the most likely cause of the thermal trip going? I've checked that there is no air in the system. By the way the circulating pump in this system is over 6 years old - is that sort of service life fairly typical for a pump?

Any advice is much appreciated!

 

[Rob]

about 10psi in the vessell, why do you think it needs charging?

system pressure should be 1- 1.5 bar cold.

it could be the pump, does everything get hot? Could be sludge in HE or faulty stat...

 

[sime10]

0.7 is ok, anything I would run it between 1 and 1.5 but thats me

 

[hammer-time]

Thanks for the reply!

I don't really suspect the expansion vessel but thought it would be a good idea to check it when I drain the system.

What's a good way to clear out sludge from the heat-exchanger? I note that this one has a little bleed tap on it but I'm not totally sure yet if that's on the cold water side or the boiler circuit side (doh!)

Yup, the system runs for a while (maybe 30 secs) gets hot and then the thermal cut out trips. Something I probably should have tried was to feel the pipe from the boiler to see if heated water was moving to the radiators.

Thanks again for the suggested pressure settings!

 

[sime10]

I don't really suspect the expansion vessel but thought it would be a good idea to check it when I drain the system.

You can test the expansion vessel without draining down

 

[hammer-time]

Thanks for that info.

I have to admit that I'm confused as I thought the system pressure of an undrained circuit would artificially increase the pressure reading of the expansion tank... so if the system pressure was 1 bar then the expansion tank would also read 1 bar, maybe it doesn't work like that?

 

[Gasguru]

Reduce the system pressure to zero. Then measure the presure oif the vessel - should be about 0.7 Bar for a normal 2 storey house. If not re-inflate but only check the vessel presure with the system presure showing zero on the gauge.

 

[hammer-time]

Ah, I'm with you now - thanks for the explanation!

 

[dan the man]

if vessel is failed it will increase dramatically when the heating does eventually work. as nowhere to expand so the pressure builds up u see. Leave some air in half a rad till u get a new vessel if so.

 

[hammer-time]

Very useful info - thanks!

I don't think the expansion vessel is leaking but I'll check it tomorrow.

The real head scratcher is trying to remove the pump as it's behind the heat exchanger and access to it is limited. Not enough space to get the pipe wrench onto the nuts - hopefully there's a suitable tool available at the heating spares store.

Don't really want to remove the heat exchanger just to replace the pump.

 

[dan the man]

sometyimes u have too..a hard life in it

 

[chrishutt]

Unlikely to be anything wrong with pump. They generally keep going for decades.

 

[Agile]

You may be able to get enough access to remove just the pump head.

If I rember correctly there is better access to the pump from underneath the boiler.

I always wonder why some people like Worcester boilers when they made monsters like that one.

Tony

 

[hammer-time]

The manual suggests that the panel under the boiler be removed and the pump be removed from underneath!

I'm not overly fond of the boiler but sometimes it's 'better the monster you know'.

P.S. Kylie once sang a song dedicated to my worcester boiler: http://www.youtube.com/watch?v=qqWeIl7UGl4

 

[Paul Barker]

I always wonder why some people like Worcester boilers when they made monsters like that one.

Tony

Me too, what a nasty boiler it is. Give me the same age group vokera any day of the week.

Worcester live on an undeserved reputation.