Boiler/central heating - replace?

[Andy Hall]

Yes.

[Roger Mills]

Better at what? Are apples better than bananas?

Sealed and vented systems each have pros and cons.

[David Hansen]

On Tue, 1 Apr 2008 04:52:39 -0700 (PDT) someone who may be tvmo wrote this:-

It depends.

[John Rumm]

In most cases yes. See Ed'd sealed system FAQ for a list of reasons why.

[tvmo]

Thanks for the replies.

Roger: you seem a little uptight. It was a general question aimed at getting personal experiences and knowledge. If you have nothing further to contribute, don't.

Cheers

[Roger Mills]

I was simply making the point (as have others) that, like a lot of things in life, there isn't a simple yes or no answer - and a lot depends on the criteria you are using to make an assessment. I hope I'm not uptight!

[David Hansen]

On Tue, 1 Apr 2008 06:42:04 -0700 (PDT) someone who may be tvmo wrote this:-

Yawn.

And in response Roger asked you a very sensible question. A question which I note you have failed to answer so far.

Were you to answer that question you would probably get some more information, though given the aggressive attitude perhaps not now.

Getting answers to general questions is what search engines are for. Having used those one can ask more specific questions.

Yawn.

Roger has almost certainly got plenty more to contribute to the group, unlike some.

[Ed Sirett]

In domestic systems I'd have to say that sealed is almost always better.

[Ed Sirett]

To a certain extent. There are only a few reasons I can think of are:

1) The existing system is correctly working and setup correctly and the new boiler would require additional expenditure to add the sealed components. 2) The existing system has radiators which are so old the designs can't take the pressure. 3) The existing system has massive 'period' radiators which have such a huge volume of primary water that a seal system would be impractical. In this case I'd recommend that the technology levels are so different that the new boiler is coupled to the old radiators via a heat exchanger and athe primary is pressurized whilst the secondary circuit is open vented.

[Doctor Drivel]

The problem with sealed system is that the filling loops are left permanently connected by installers - not supposed to be. Some are a part of the boiler too. When the expansion vessel deflates, or a leak, the user just tops it up by turning the tap. This leads to water gushing out of the discharge pipe, sometime onto public walkways. And the users will do this for months and years, especially those in rented property. It also introduces fresh water into the system and accelerates corrosion. Sealed system expansion vessels fail eventually - usually sooner than later. Sealed systems are intolerable of minute leaks too. I know of some systems where a small leak was never found after extensive searching. The pressure eventually drops and a service call.

A one pipe system with a close fitting lid F&E tank is generally the better option in reality. Sealed systems are great when installed properly and don't go wrong. The expansion vessel prevents pump cavitation too and quietens pump operation too.

[John Rumm]

That is not a problem with sealed systems. It might be a problem with some installers.

Clueless people can cause problems with any installation. They are just as likely to leave a header tank system pumping over for years.

Plenty of people seem to mange for twenty years or more without any problem...

Which is another advantage of the sealed system.

I know of a vented system where a small leak was never found until several years later when a substantial dry infestation was discovered. I know which I would rather have.

For some versions of reality perhaps...

Plus no problems with air locks, or difficulties refilling the system etc.

[Roger Mills]

I would have to agree that sealed systems provide a better techical solution in preventing pumping over and air locks - but there is rather more to go wrong. They are less tolerant of slight leaks, and failure of the expansion vessel causes a whole raft of problems.

It would be interesting (but I ain't going to do it! ) to see an analysis of all the posts here which report problems with CH systems, and showing what proportion are sealed vs vented.

[Doctor Drivel]

It is a big prblems with sealed system.

A sealed systems happen to be one in big way.

Very rare.

Most do not.

[John Rumm]

The system works perfectly with the filling loop connected. Its only if some muppet starts filling it to mask some other problem that it is an issue. That's not a problem with sealed systems. In the same way that someone setting the pump speed too high on a vented system and causing pump over is not an inherent problem with the vented system, but a problem with its installation.

Again in English?

So someone that is clueless enough to not spot water pouring out of the PRV every time the system gets hot, and topping up twice a day is however going to correctly identify, diagnose and rectify a pumping over problem?

If you believe that you are barking.

Most systems work fine most of the time. Its only a small proportion of systems of any type that go wrong, so you comment (as usual) make little sense.

[tvmo]

Whether I was aggresive or not (apologies if I was) or Roger's comment about apples/bananas were flippant/uptight or not (sorry if I read it wrong), the thread seems to continue.

David Hansen: I won't labour on your points....yawn.

I read with interest the different point of views and I'm learning lots that you don't pick up by just reading articles.

Thanks all.

[John Rumm]

Don't think you were aggressive - there are worse culprits here! ;-)

Roger can be relied on to give considered and useful advice, I think you may have just read it the wrong way.

Yup, much to be said for a bit of disagreement since it can take the thread into new and interesting areas that otherwise would remain uncharted.

[Doctor Drivel]

If the check valve fails it spurts contaminated water into the drinking water mains.

Which is common.

It is, if the system were not sealed and configured as they are it would not happen.

A rare problem.

[John Rumm]

if... if... if...

if the tap is also left open, and the mains also suffers a drop in pressure so that it is lower than that stored in the system.

Tap off, double check valve in place, loop connected. Common occurrence, no risk to system or water main.

you're repeating yourself dribble...

lol!

[Doctor Drivel]

Yes, if. Murphy's law says.....

It is, if the system were not sealed and configured as they are it would not happen.

You know sweet FA about heating systems in the real world.