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      12-23-2012, 03:52 AM   #1
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Combi boiler advice - pressure keeps going down

Hi guys.

Quick one - the pressure on my boiler keeps going down - I presume it's a sealed system. I put more water in quite regurally so the water must be going somehwere.

Does this definately mean a leak? Nothing is coming through the ceiling so if the pipes are leaking it must be under the floor on the ground floor - if this is the case then I'd imagine that finding it would be a major job!

I know nothing about boilers but I'm hoping a sealed system has some kind of saftey outlet - perhaps this outlet is slightly open? If this is the case, where would the water go? There's no overflow pipe on the outside of my house.

Thanks in advance for any comments
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      12-23-2012, 05:16 AM   #2
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Quote:
Originally Posted by BanziBarn
Hi guys.

Quick one - the pressure on my boiler keeps going down - I presume it's a sealed system. I put more water in quite regurally so the water must be going somehwere.

Does this definately mean a leak? Nothing is coming through the ceiling so if the pipes are leaking it must be under the floor on the ground floor - if this is the case then I'd imagine that finding it would be a major job!

I know nothing about boilers but I'm hoping a sealed system has some kind of saftey outlet - perhaps this outlet is slightly open? If this is the case, where would the water go? There's no overflow pipe on the outside of my house.

Thanks in advance for any comments
Yes it is sealed. If it is leaking it tends to be joints that go first so check all the rads first. Water can seep out the valves and runs down the pipe so is not obvious. Also is there inhibitor in the water as if not you get corrosion inside the rads and this gives off gas which loses pressure. Check the bleed valves on the top of the rads as well.
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      12-23-2012, 06:59 AM   #3
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I doubt you've got a leak Banzi,your problem sounds like a classic case of the expansion vessel losing it's charge (pressure)'

I have a Combi,and this used to happen regularly,basically the system is sealed,so when either the CH gets warm/or your using the hot water,the water heats up and expands,but has nowhere to go to,hence the expansion vessel.
Imagine a football is the expansion vessel,the football is divided into two sections by a membrane,one half is for the water to expand into,the other half is pressurised (charge).
As the water in the system expands through heat,the membrane in the 'football' expands and contracts and is supported by the pocket of air on the other side of the membrane.

As that charge/pressure is no longer present,the water now has nowhere to go, so will be discharged out through a blow off valve,which normally goes out of a pipe to the outside of the house.
The above is why you're constantly topping up the system.

So,the solution is to either charge the system yourself, or get a CH engineer to do it.
It shouldn't take an engineer/plumber more than 15 mins max to sort,so shouldn't be too expensive.

and breathe........................
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      12-23-2012, 07:02 AM   #4
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Sounds like the EV, our most common fault.

If you have access to the expansion vessel valve (looks like a car tyre valve) it should be around 21psi when measured.

Also check the pressure relief pipe if its letting water by it'll also need replacing.
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      12-23-2012, 10:44 AM   #5
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Great! Thanks. Getting a new boiler in March so I'll wait - looks like I won' t be having to take my floor up then

Cheers!
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      12-23-2012, 01:44 PM   #6
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Looks like we're lucky to have a couple of well-versed heating engineers on here!
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      12-23-2012, 03:07 PM   #7
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Looks like we're lucky to have a couple of well-versed heating engineers on here!
For sure! Great source of knowledge this place.
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      12-23-2012, 03:34 PM   #8
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Hmmm. sounds like a leak.

How often do you fill it? what pressure does it drop to and what pressure do you refill it to? Is yours an old house with old rads/pipes from gravity fed pre-combi days?

Does it drop even if the heating is off?

The overpressure valve won't release until at least 3 bar, so if its the EV you'll see the pressure go up when the heating is on, then it would blow off at 3 bar or so. If the pressure only goes up a little when the heating is hot then it ain't the EV...
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      12-23-2012, 04:00 PM   #9
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Yeah, it drops when the heating is off, and goes up again when it's on.

When the heating is off the gauge is right down at virtually nothing - I fill it about once a week to get the pressure up to about 2 bars when the heating is on.

Question: should the gauge be showing running pressure or 'boiler off' pressure? I.e - should I charge the boiler up so that it shows 2 bars when it's not running?

A few months ago there were some drips coming from the actual boiler but that has stopped since so this doesn't seem to be the problem.

I'm pretty sure the the rads were installed with the boiler about 15 years ago.
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      12-23-2012, 05:41 PM   #10
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Quote:
Originally Posted by BanziBarn View Post
Question: should the gauge be showing running pressure or 'boiler off' pressure? I.e - should I charge the boiler up so that it shows 2 bars when it's not running?
I'm pretty sure the the rads were installed with the boiler about 15 years ago.
Banzi,you need to refill the system when it's cold & off.

Filling when the system is running is not recommended,as the water in the system is already hot,therefore expansion will have already taken place,and any reading you get from the pressure gauge will not be accurate.

My Combi's instructions state a pressure of 1.5bar when cold and off.

I would have thought that were there leaks within the system,at 15 odd yrs of age,the leaks would have shown up by now.

A fairly reliable way of finding out if it is the expansion vessel causing the problem,is to locate the discharge pipe.

It should be located near the flue pipe,which comes out of the external wall,normally behind the boiler,the discharge pipe is a 15mm pipe and looks like a overflow pipe on a toilet.

If you find the discharge pipe,tie a see through plastic pipe over it,but DON'T make it air tight.
If the bag collects water,it's because the system is overheating,and because the expansion vessel has lost all it's pressure the membrane within can't expand, so the heated water will get kicked out through the pipe,and go in the bag.

If water gathers within the bag,that's the water that has escaped the system,that has resulted in your pressure loss.

PS,I'm not a plumber,nor heating engineer,but I have had Combi's since they first came on the market,and I've had my fair share of problems with them, and where possible,I like to fix them.
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      12-24-2012, 03:42 AM   #11
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It shouldn't really change much from cold to hot if the EV is doing its job properly.

In my experience, say 1.5 cold to 1.7 hot.

What does it rise to when hot?
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      12-24-2012, 04:05 AM   #12
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Not really sure - I've not pressurised it when cold before so it's probably not a fair test.

It's now set at 2 bar at cold so I'll keep my eye on it and see what it does!

Thanks for all your help guys.
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      12-24-2012, 04:57 AM   #13
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Great this place, you can find out almost anything and be pointed in the right direction by just asking fellow forum members for a bit of advice.

We still have a old condenser boiler [ think thats what its called] and a few mates have told me they wished they had stuck with these instead of going for a combi, i thought the combi boilers are better and more fuel efficient ? We need to replace ours soon and not sure which to buy.

sorry for hijacking OP but seemed silly to ask this on a seperate thread.

Happy Christmas
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      12-24-2012, 05:13 AM   #14
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I think, and I may be wrong that the condensing part isn't connected to having a combi or not.

Condensing was the new 'thing' which made boilers more efficient and all are now condensing. Whether you go for a combi or not, it's till condensing.

Combi is convenient because you only heat the water you need, and you can get rid of your tank (useful in my case as I'm having a loft conversion). Plus you have an endless supply of hot water.

But, if two people want a shower at the same time, a combi won't be as good as it may not be able to heat enough water.

Please correct me if I'm wrong... which I probably am!!
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      12-24-2012, 05:32 AM   #15
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Quote:
Originally Posted by BanziBarn View Post
I think, and I may be wrong that the condensing part isn't connected to having a combi or not.

Condensing was the new 'thing' which made boilers more efficient and all are now condensing. Whether you go for a combi or not, it's till condensing.

Combi is convenient because you only heat the water you need, and you can get rid of your tank (useful in my case as I'm having a loft conversion). Plus you have an endless supply of hot water.

But, if two people want a shower at the same time, a combi won't be as good as it may not be able to heat enough water.

Please correct me if I'm wrong... which I probably am!!
It's a long time since I've looked into the benefits of a condensing boiler,but I think it's now the case,as Banzi stated, that all boilers regardless of type are condensing.

Banzi's pointed out the benefits of instant hot water from a combi,+ not having to have a water tank in the loft/elsewhere,but the biggest pitfall of Combi's,as Banzi also pointed out is that that when using other things that place demand on the water,be it hot or cold,someone in the shower will lose the pressure from the shower head,and get fecking cold!

I suppose if you have the normal family 2 adults +2.5 children (what the feck is the .5?Never understood that),and you all do things first thing in the morning (the norm),it's annoying when the water pressure in the shower disappears in the middle of washing your hair,shampoo in the eyes is fecking painful!

So,in some cases,a Combi is not always the best option.
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      12-24-2012, 06:46 AM   #16
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I have a special shower that automatically maintains the temperature - so if someone puts the washing machine on mid shower, the pressure will reduce yes, but the shower will adjust the temperature to avoid you getting scaleded... which is nice

I only have one shower, but I'll have two next year along with a new boiler, but I'm expecting it not to work that well if two people want to wash at the same time.

Question: I know you can't get a pumped power shower if you have a combi boiler, but can you put a pump on the water supply that feeds the boiler? Obviously this would rely on a boiler being able to heat a higher flow of water, but if you had such a boiler, would that work?
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      12-24-2012, 06:56 AM   #17
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Quote:
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Question: I know you can't get a pumped power shower if you have a combi boiler, but can you put a pump on the water supply that feeds the boiler? Obviously this would rely on a boiler being able to heat a higher flow of water, but if you had such a boiler, would that work?
I don't think what you're thinking about would work Banzi.

Most Combi's will only supply a max flow rate based on what the burner will cope with,pushing more water through would probably not be possible,as the boiler will probably limit the amount of pressure that it will accept.

Worth checking out I suppose,pop into a Plumbers merchants,they could advise better than me.
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      12-24-2012, 07:47 AM   #18
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2 showers? I am pretty sure you would need a condensing boiler.

If at not at the very least you will need a hot water tank in an airing cupboard and a cold water tank in the loft mate. Basically a gravity fed system.
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      12-24-2012, 08:16 AM   #19
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2 showers? I am pretty sure you would need a condensing boiler.

If at not at the very least you will need a hot water tank in an airing cupboard and a cold water tank in the loft mate. Basically a gravity fed system.
All boilers now are condensing AFAIK.

Yeah, a tank would be better I agree, but there won't be any room for a tank to be installed once we get our loft converted, and also the cost to install would be too much for us.

Regarding the max flow rate of the combi boiler - I guess I would need to check as to whether my mains pressure is up to max that the boiler can cope with - if not, perhaps a pump could bridge the gap?
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      12-24-2012, 08:34 AM   #20
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What you need Banzi,is your own personal wet room with it's own small Combi,which just provides water to the the shower,and it's own water supply direct from the mains, bliss!


Quote:
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Regarding the max flow rate of the combi boiler - I guess I would need to check as to whether my mains pressure is up to max that the boiler can cope with - if not, perhaps a pump could bridge the gap?
Yep,finding out what the mains pressure is coming into the house would be useful,but I don't think a pump would make much difference.
It can only pump what's available to pump,so if the mains pressure is 8bar,adding a pump wouldn't make more water available,or would it?

I'm starting to dfift out of my knowledge base here,when that happens,I tend to talk bollocks,so feel free to ignore me.
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      12-24-2012, 08:43 AM   #21
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Sorry mate I meant Heat only Boiler. This way the hot water is stored in a tank and there is flutaution in water temperature when you run a shower and run a cycle on the washing machine.

I am not a plumber mate. What I do know is that our house is a 6 bedder with 2 en suites.

What we do is a Heat only boiler in the downstairs utility room. There is a pump upstairs in the Airing cupboard which pumps the water from downstairs into the hot water tank.

We then have a 2 bar pump under the bathtub. This pumps hot water from the tank in the airing cupboard and cold water from the tank in the loft into our high flow shower.

We were attracted to fitting a combi boiler initially but were advised against it by a few plumbers who said basically we had to have a gravity fed set up.

Thats all i know.

What I am wondering is, if you have a pressure issue which I am sure would be easy ( hope so) to fix. I am wondering if you are planning on setting up the second shower in the loft? In which case are you sure your combi will be able to cope? I am not sure it will.

using deductive logic ( again i am no plumber). You wont be able to put a pump from the mains into the combi boiler. ASFAIK pump makers prohibit fitting shower pumps to the mains. Usually you can only fit these after the boiler or after a tank?

Secondly fitting a pump in the loft ( if that is what you are going to do) will only magnify the issue of flowrate.

1. if by any chance you can buy a pump to the boiler. It can only heat water at a certain rate.
This would be the issue people have with those little electric showers. They heat the water and push it out the head but whilst the flow is ok its never super powerful is it?
2. Even if you put a pump in the loft for the shower, you will be pulling water up faster than it can be heated?

Or am I missing something here?
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      12-24-2012, 08:44 AM   #22
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Yea feel free to ignore me too
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