Combi Boiler problems.

[rizla01]

Hi All.
Apologies in advance for the lengthy story.

Like most of us, I like a problem and the satisfaction of solving it and felt capable of doing so as I have had some plumbing experience (Pre Corgi) and have, in fact fitted a complete system around 20 yrs ago (Tho my mate, Bill the Plumber did the final checks)

Here begins. About a month or so ago, my 9yr old Main Eco30 Combi stopped working. No heat and no hot water.


I checked and seeing the pressure gauge had dropped, repressurised using the FIXED loop, to around 2Bar. Went round and bled the system and found a little air in the system after which the pressure dropped to about 1.5 bar. Fine for a week or two then it stopped working again.


Re-pressurised again and that lasted about 24 hours before needing to be once again Re-pressurised.

Checked a few forums and decided I needed to change the Pressure Release Valve to eliminate that as the cause. No probs as they are less than £5 on ebay. I decided to drain the whole system as the bottoms of the rads always seem quite a bit cooler than the rest (Took about 4 hours as a couple of rads are fed by micro-bore). No real sludge emerged tho.

I needed to slightly modify the pipe work to fit the kungfoo copy pressure valve as the dimensions were a slight difference, but having done that was up & running in no time.
I purposely closed both valves on the towel rail so that I could add inhibiter once I was satisfied that the problem had gone away.

After around 2 weeks felt I could safely do just that. WRONG!! A week later no pressure again??

I carried on Re-pressurising every morning whilst deciding what to do then decided to have a go at the Expansion Vessel. Took it to 14.5 PSI having found no pressure (At least I dont THINK there was) and that fixed it.
Feeling a bit paranoid, I kept looking at the gauge for almost a week before feeling comfortable and that I had finally cured the problem. Just beginning to relax and deal with other problems in life and....Wait for it...
Last week (After about 2 more weeks) it went yet AGAIN!!!!

Re-pressurised once more and that lasted 24 hours and I have had to re-pressurise it again this morning. - Ok. Now what?

I am thinking that the system is over pressurising and blasting the water past the valve a few times when it gets too hot and then eventually there isn't enough water left in the system?

From what I have read, it seems it could be a pinhole in the Diaphragm of the pressure Vessel or a small leak in the heat exchanger (Evaporating before it shows) then over heating, losing water and then losing pressure.

I feel a failure here and am now considering calling in 'The Man' as, although I could change the pressure vessel, it might not be that and an engineer can test parts that I am not able to and obviously he should be better able to spot the problem as he should know where to look.
Is it now time to hand over the reins?

Any thoughts or observations?

 

[NazNomad]

I know from my own boiler that the 'failing' diaphragm in the expansion vessel caused the pressure drop on my Worcester Bosch.

 

[Gerry]

If you keep an eye on the pressure gauge while the heating is running and see the pressure slowly swing up and down with temperature then this indicates a faulty expansion diaphragm. With a good expansion vessel the pressure will remain near enough fixed as it compensates for pressure variation.
If the expansion vessel is integral to your boiler you have two choices. either remove the boiler and fit a replacement or fit a remote vessel (much cheaper) to the CH return and leave the old one in place.

Gerry

 

[rizla01]

If you keep an eye on the pressure gauge while the heating is running and see the pressure slowly swing up and down with temperature then this indicates a faulty expansion diaphragm. With a good expansion vessel the pressure will remain near enough fixed as it compensates for pressure variation.
If the expansion vessel is integral to your boiler you have two choices. either remove the boiler and fit a replacement or fit a remote vessel (much cheaper) to the CH return and leave the old one in place.

Gerry

If I leave the old one in place do i need to do anything with it or just pretend it isn't there?
It is internal and easy enough to get to but like you say - double the price.

 

[Fitzroy]

I had a similar issue on my system, i'd had a new boiler 5 years back and the system changed to a pressurised combi rather than a gravity fed, tanked back boiler thing. For a few years everything was ok, i made some other mods, added radiators and a secondary expansion vessel. A couple of months back the pressure started dropping off, and I had to refill occasionally. However it was not a systematic loss, ie at times the pressure would stay for a week, then be gone overnight., so I assumed it was a relief valve etc.

I investigated all my modifications and found a couple of tiny leaks (radiator valve, and underfloor manifold to new rads), fixed them but the problem prevailed. I finally started lifting floors (my house has suspended timber floors) and I then found a puddle. Finally I located an old low point drain valve that I did not know existed, it was less than hand tight, and depending on how I twisted the handle it would drip or trickle water out. I tightened it once as best I could, then two weeks later the same again, went back to it and it was leaking again. I had to life a carpet and floor in another room to get enough access to tighten it correctly, corrosion on the stem meant it required working open and closed to get it properly closed. That was a few months back and now everything is bob on, not topped up the system since then.

Long story, but moral is leaks can appear in the most unbelievable places and they are not always consistent.

F.

 

[Gerry]

If I leave the old one in place do i need to do anything with it or just pretend it isn't there?
It is internal and easy enough to get to but like you say - double the price.

Just leave it alone, It doesn't have any effect on the system once the diaphragm is porous

Gerry

 

[Eric The Viking]

You said it's a combi: hard or soft water area? If hard, do you have a softener unit on the incoming cold feed to the boiler?

Also, if you fill it cold to around 1.5-2 bar, how quickly does the cold temp drop off to less than 1 bar? Hours, days...?

 

[Keithie]

I had a very similar thing indeed (having to top up the pressure increasingly often) at my previous house with an old Vaillant boiler. Solution ...sell house

Seriously though, it did end up with a replacement pump (and tweaking of radiator valves etc) which seemed to sort the problem (though I've no idea why /how) and we did sell less than a year later so it's not clear if the pump was really the core problem.

 

[rizla01]

You said it's a combi: hard or soft water area? If hard, do you have a softener unit on the incoming cold feed to the boiler?

Also, if you fill it cold to around 1.5-2 bar, how quickly does the cold temp drop off to less than 1 bar? Hours, days...?

Presently lasting almost two days before boiler cuts out and needs topping up.
No softener unit fitted.

 

[Eric The Viking]

Hard or soft water area?

You haven't told us your location, so I can't guess...

 

[rizla01]

Hard or soft water area?

You haven't told us your location, so I can't guess...

I am in Essex.
Not sure but i think its a hard area.

 

[jimmy_s]

It could be a pin hole in the expansion vessel diaphraghm if so there will be nowhere for any expanded water to go when the water in the heating system heats up and the safety valve will lift. If you can put a bowl or something under the safety valve discharge pipe you will find out if its blowing. Also if that's the problem the diaphragm in the exp vessel will be empty the vessel will be full of water and normally if you depress the pin in the schraeder valve you will get water out rather than air.

 

[Paul200]

It could be a pin hole in the expansion vessel diaphraghm if so there will be nowhere for any expanded water to go when the water in the heating system heats up and the safety valve will lift. If you can put a bowl or something under the safety valve discharge pipe you will find out if its blowing. Also if that's the problem the diaphragm in the exp vessel will be empty the vessel will be full of water and normally if you depress the pin in the schraeder valve you will get water out rather than air.

Yep. I was about to say that. Had this with a Saunier Duval boiler down south (don't EVER buy one!). The plumber was really p'd off that he had a load of water through his pressure meter - made me feel like it was my fault!

 

[rizla01]

It could be a pin hole in the expansion vessel diaphraghm if so there will be nowhere for any expanded water to go when the water in the heating system heats up and the safety valve will lift. If you can put a bowl or something under the safety valve discharge pipe you will find out if its blowing. Also if that's the problem the diaphragm in the exp vessel will be empty the vessel will be full of water and normally if you depress the pin in the schraeder valve you will get water out rather than air.

When i re-pressurised the expansion vessel there was no water but I am told that if it is just a pinhole that the small leak can evaporate before it shows.

The PRV is definitely letting past until the pressure drop is very low but that can take two days.

 

[John15]

I had a loss of pressure on my boiler - rats/mice had chewed through an HDPE fitting below the floor.

John

 

[Eric The Viking]

You may well be in a hard water area - if I remember my school geography lessons of 50 years ago, London water used to come from a chalk aquifer via boreholes. I know a lot of it is recycled these days, but there's probably still quite a lot of hardness (calcium carbonate, IIRC).

It does all sorts of expensive damage. At the 'merely annoying' end, it makes kettles noisy and destroys chrome plating on taps, etc. It also damages plastic piping in hot water systems (the flexible type, with braided outer: i've no idea about the stuff presently used for pipe runs), and I'd guess it can aid in the formation of pinholes and fractures in diaphragms, such as the ones in cistern valves (Torbeck, etc.) and presumably pressure vessels too.

But what I was thinking about in the main is the diverter valve found in combi boilers. This uses the drop in hot tap water pressure inside the boiler to move a valve to divert your radiator water through a secondary heat exchanger inside the boiler to instantly heat the tapwater. Designs may have changed, but the ones I've seen in the past have had a diaphragm and a piston, similar to a trumpet (musical!) valve - moving a central piston changes the routing of pipes.

They're complex, hard to seal, and vulnerable to limescale. Then they leak, either internally (between the different sections of the valve) or just drip. That's the main reason why combis should have softeners fitted to the cold water inlet.

Anyway it's one place inside the boiler where you can get trouble. Boiler leaks are difficult, because the water evaporates. You might diagnose a bit though. As suggested, put something under the safety overpressure valve outlet (usually goes to the outside of the house) to see if it's operating.

Those valves, incidentally are themselves a source of problems. The one in my boiler is mounted upside down, so any carp in the pipe gets trapped in the body of the valve. If it operates for any reason, it then won't reseal properly but just dribbles, as the grit or whatever stops it resealing.

Check that. If they're over a drain, plumbers often use them to depressurise the system quickly to work on it. Did you have to top-up before you first turned the heating on in the autumn, or during the summer when it was just doing hot water?

The other thing is just have a good look around the inside of the boiler with a torch and a mirror on a stick: are there any signs of leaking - stains on the inside base of the cabinet, or crusty bits near joints?

The other thing is in extremis, you can make use of an "off" radiator to substitute for an expansion vessel - not a permanent solution, but...
... seal off the taps, drain off a bit of water so that there is an air space in the rad (open the air vent). once you have a decent amount of air in it (no more than half empty). seal up the joint and close the air vent, and re-open just one tap. I'd open the return side (if you know which it is), as that water should be slightly cooler, giving you slightly lower pressure in the rad. When you can sort out any damaged pressure vessel (replace or add another) , you simply bleed the rad so it's properly full again.

If the pressure is fluctuating as the system heats up and cools down, that's a pressure vessel problem.

 

[rizla01]

You may well be in a hard water area - if I remember my school geography lessons of 50 years ago, London water used to come from a chalk aquifer via boreholes. I know a lot of it is recycled these days, but there's probably still quite a lot of hardness (calcium carbonate, IIRC).

It does all sorts of expensive damage. At the 'merely annoying' end, it makes kettles noisy and destroys chrome plating on taps, etc. It also damages plastic piping in hot water systems (the flexible type, with braided outer: i've no idea about the stuff presently used for pipe runs), and I'd guess it can aid in the formation of pinholes and fractures in diaphragms, such as the ones in cistern valves (Torbeck, etc.) and presumably pressure vessels too.

But what I was thinking about in the main is the diverter valve found in combi boilers. This uses the drop in hot tap water pressure inside the boiler to move a valve to divert your radiator water through a secondary heat exchanger inside the boiler to instantly heat the tapwater. Designs may have changed, but the ones I've seen in the past have had a diaphragm and a piston, similar to a trumpet (musical!) valve - moving a central piston changes the routing of pipes.

They're complex, hard to seal, and vulnerable to limescale. Then they leak, either internally (between the different sections of the valve) or just drip. That's the main reason why combis should have softeners fitted to the cold water inlet.

Anyway it's one place inside the boiler where you can get trouble. Boiler leaks are difficult, because the water evaporates. You might diagnose a bit though. As suggested, put something under the safety overpressure valve outlet (usually goes to the outside of the house) to see if it's operating.

Those valves, incidentally are themselves a source of problems. The one in my boiler is mounted upside down, so any carp in the pipe gets trapped in the body of the valve. If it operates for any reason, it then won't reseal properly but just dribbles, as the grit or whatever stops it resealing.

Check that. If they're over a drain, plumbers often use them to depressurise the system quickly to work on it. Did you have to top-up before you first turned the heating on in the autumn, or during the summer when it was just doing hot water?

The other thing is just have a good look around the inside of the boiler with a torch and a mirror on a stick: are there any signs of leaking - stains on the inside base of the cabinet, or crusty bits near joints?

The other thing is in extremis, you can make use of an "off" radiator to substitute for an expansion vessel - not a permanent solution, but...
... seal off the taps, drain off a bit of water so that there is an air space in the rad (open the air vent). once you have a decent amount of air in it (no more than half empty). seal up the joint and close the air vent, and re-open just one tap. I'd open the return side (if you know which it is), as that water should be slightly cooler, giving you slightly lower pressure in the rad. When you can sort out any damaged pressure vessel (replace or add another) , you simply bleed the rad so it's properly full again.

If the pressure is fluctuating as the system heats up and cools down, that's a pressure vessel problem.

Hi Eric.
Thanks for that nicely detailed explanation.

Fact is that SOMETIMES the hot water is luke warm depending, I have found, on whether the CH system is calling for heat. I suspected the diverter valve but as it only happens at certain times, I would live with that. I didn't figure that this could also be the cause of the later problem.

I am pretty sure that there has never been any inhibitor in the system either.

Biggest pain in the 'arris is that since last year I have wanted to sell up and move so extra hassle & expense is irritating, to say the least, but I cant give the new owners a problem to start with.
(Its a known fact that houses do that when you want to sell them, you know - they understand these things).

 

[rizla01]

Unbelievably my system hasn't stopped working since last time i repressurised it about 5 days ago now.

Being forced to study my system now, I do note that many times the hot water is only warm, more often than before but, despite even colder weather (working harder) its not needed looking at.

Could it just be a kit for the diverter valve that is needed and would that somehow cause over-pressuring of the system or do I have two issues going on here?

 

[NazNomad]

The only probs I've ever had with the diverter valve caused the rads to get hot when only the water was on. Not sure it could affect pressure, but I dunno.

 

[Gerry]

I had issues with my old baxi combi where occasionally the water would only get luke warm. It turned out to be muck in the heat exchanger, the black sludge you sometimes find in radiators had circulated through the system and clogged the exchanger. I managed to remove it by draining and pressurising the system a few times at weekly intervals so the dirt was getting washed out of the heat exchanger and in to the rads.
Black sludge is a killer for combi's.

Gerry