Combi-boiler losing pressure

[Jason]

Our Ideal Response 120 has started losing water pressure, and needs to be topped up several times a day. I've checked all the pipes under the ground floor, and cannot find a leak. There are no tell-tail stains in the ceilings, so I doubt I have a leak up there.

I put a plastic bag over the pipe that sticks out the wall from the boiler, and that caught about a tablespoon of water as the pressure dropped from 1.5 bar to 0.5.

So far as I can tell, the pressure is stable for a few hours, then suddenly drops. Is this likely to be a fault, or can this be caused by my system being gunged up? I can imaging that clogged up pipes, like arteries, would cause high pressure when the pump runs, and could result in some venting - but I'm just guessing now.

Would emptying the system be something I can do myself, or are there important repriming steps that only a pro would be able to do (or would know was done right)? Would simply draining and refilling actually make any difference anyway? Any other DIY checks I can perform, before calling in the Corgi-registered plumbers?

-- JJ

[Roger Mills]

Why do you need a Corgi registered plumber - I thought you had a water leak, not a gas leak?!

A tablespoonful of water wouldn't normally account for a 1 bar drop in pressure - you'd need a couple of litres or more - although this would be reduced if the system had no expansion capacity.

Chances are that you've got a problem with the expansion vessel. It could be shot and need replacing, or it could simply have lost its charge (air) pressure and need re-charging.

Start by finding the expansion vessel, if you don't already know where it is. It may be bomb shaped, or - if it is inside the boiler casing - it may be pancake shaped. It should have a schrader valve (like a car tyre valve) for pressurising it and checking the charge pressure. With the water system

*unpressurised*, measure the charge pressure with a car tyre pressure gauge. [If water comes out of the valve, the vessel is shot and will need replacing]. The pressure needs to be in the region of 0.7 bar (about 10 PSI). If it isn't, pump it up with a car tyre pump. Then use the filling loop to pressurise the water system to 1 bar with the system cold. With any luck it should then be ok.

[Jason]

It's the bomb-shapped variety, on the RHS behind the enormous collection of controller boards. Very kindly, Ideal have provided a little panel on the top to give access to the charge nipple. No water, and definately some air pressure in it, so I'm keeping my fingers crossed there.

When you say the system should be unpressurised before charging up the expansion vessel, does that mean I should remove a little water from the system to bring the pressure down, or do I need to go as far as turning off all the radiators and draining them right down? What I mean is, would the pressure of the water in the upstairs radiators and pipes be enough to spoil the measurements?

Also, I assume it does not matter if the system is still slightly warm when I do this.

-- JJ

[block]

hi,

Could be the heat exchanger has a leak. this happened to my response 120 and i had to replace it.

[John Stumbles]

Not if he says the pressure stays OK: if the expansion vessel were the problem the pressure would go shooting up and open the pressure relief valve (PRD). Sounds as if the PRD is incontinent and needs either wiggling the knob/lever a few times to get it to seat properly (if you're lucky) or replacing.

[Jason]

I'll watch out for that, but I've charged up the expansion tank for now, and hopefully that will fix it.

I repeatedly pumped up the tank a bit, then released some water, then pumped it up a bit more, then released some pressure. The pressure at the pump and on the front panel went up and down together, until it suddenly reached a point where the tank pressure was increasing, and the water pressure stayed at zero. So the result was the tank was pressurised to 0.7 bar with the water at negligible pressure.

The tank took a lot of air, and I suspect it was almost entirely full of water. I emptied nearly a bucket of water out of the system, to keep the pressure at zero, from the point where I started pumping air in.

Thanks for the help, Roger. A beer is waiting for you in Newcastle :-)

-- JJ

[Jason]

The tank was definately just about full of water (estimated by the amount of water I had to remove from the system to pump it back up). With a little luck that was the only problem (but if there is one thing I know about heating systems, is that seldom does just one thing go wrong! The Raven boiler at the office has taught me that.)

Anyway - something else for me to check if problems continue.

-- JJ

[Ed Sirett]

With this boiler the thought is always "Is the heat exchanger leaking yet?" The second is "How badly is it leaking now?"

8-(

[Jason]

Okay - I'll see if I can get my hands on a spare one, in preparation for the enevitable (I've got family at Caradon-Mira who can probably get me a good deal on one).

-- JJ

[Roger Mills]

It sounds from your other posts as if you've sussed it, anyway. But you just need to let sufficient water out to ensure that the gauge reads zero, thus ensuring that the expansion vessel will be completely full of air when you charge it. If the water pressure is higher than the air pressure, there will still be some water in the vessel.

If it's only *slightly* warm, it's not a problem, but you then need to set the water pressure to slightly over 1 bar - otherwise it may fall too much when it cools. It's probably ok to set it to 1 bar when slightly warm, and then re-check and adjust it when it is fully cold.

If your vessel was full of water at all times, the system would have had no expansion capacity - so the pressure would rise very rapidly - and open the safety valve - whenever it warmed up. Hopefully what you have done will now have fixed it.

Whereas a spare heat exchanger may be a good idea, a leaking heat exchanger would not cause your expansion vessel to fill with water - so that's unlikely to be the immediate cause.

[John Stumbles]

Thanks Ed. BTW how's that boiler fault-finding FAQ coming on?! And are you going to name names and include stock faults?

[Ed Sirett]

Right now I've run out of steam (perhaps for 11 months), my other FAQs were prepared around the post Festive Season period.

I've roughed out the 'how not to kill yourself stuff' and 'how to be methodical in diagnosis' drawing heavily on "Silicon Sam" s.e.r.faqs.

I've more or less completed the "low tech"[1] boiler (Baxi Bermuda 551) description. That leaves the "middle tech" [2] boiler (Pott. Profile 60e). That will introduce the idea of electronic ignition and sequencing controls.

I have a bit of difficulty selecting the candidate for the high tech [3] boiler. In order to span the range of technologies in their most common forms it needs to be a forced premixing burner condensing combi with a DHW diaphragm operated diverter valve. Is the latest Worcester Combi like that? I've so far only fitted the system version. I know the Vail. Ecotec well but it uses a small permanent magnet turbine and Hall effect probe for DHW switching. The need to fully describe 3 different models is that there have been such significant qualitative jumps in the tech levels in just 30 years that really boilers in each different class are essentially a completely different machine, common only in that they burn gas and heat water.

As for naming names I will stick to generic stock faults like what happens if the DHW flow detector diaphragm splits (which they do a lot). What goes wrong in general with component X is Y, how you tell that this is the case and what you can do about it.

We can name names on the uk.d-i-y

[1] Low tech - no electronics [2] Middle tech - electronics but no software. [3] High tech - electronics and software.

[John Stumbles]

That sounds worth having on its own. G'wan: show & tell! :-)

Even if it's flagged as being a work-in-progress it would avoid duplication eleswhere. It's the sort of thing I'd be inclined to cover when (hah!) I've done the CH fault-finding I started on the wiki

I've more or less completed the "low tech"[1] boiler (Baxi

I don't think so: it claims to have a flow turbine. (I haven't had to deal with one in anger yet.)

I guess diaphragm valves are just *so* last year now :-)

Does it have to be a detailed description of one particular model? I tend to think in terms of what subsystems has this machine got and how do they go wrong.

Not sure I care about the software - from the fault-finding point of view I tend to think of boilers in terms of

[1] permanent pilot light, thermocouple interlock, fanless [2] ignition-on-demand, fan + air-pressure switch, overheat cutout, some sort of PCB (to go wrong!) [3] modulating standard efficiency or high efficiency (definitely RTFM!)

Then I factor in whether it's a combi and what sort - diverter valve + PHE or combined combined primary+DHW gas/water heat exchanger (like Worcester non-CDi models).

That gives a fair number of permutations (or is it combinations?)

I'm thinking that full descriptions of 3 models is going to leave an awful lot of exceptions e.g. if one describes a 'typical' combi with PHE and diaphragm diverter valve how is Fred Bloggs going to know that he's not looking at a split diaphragm when he isn't getting any DHW from his Worcester 24i?

It'd be useful to have a cheat list in one place somewhere e.g. your mention of the leaky heat exchanger on this model which I didn't know about, Suprimas (obviously), Barcelonas, Profile overheat stat tripping, that business with the Ravenheat cycling ... etc etc. Useful info like this tends to be drowned in the noise when googling. Could go on the wiki.

[Ed Sirett]

OK The main TODO area would be to fix up all the links. The safety stuff really is rather patronising but was fairly easy to lift from Silicon Sam.

and put it in the wiki.

They are so reliable that I've only had to deal with one so far, and that one always fixed itself as so a the cover was removed so took a while to track down.

Vaillant would say they were *so* last millennium.

The reason for doing this is so that a reader can read the FAQ together with the installation Manual PDF which provides diagrams and pictures.

I'm certainly with you on the [1] and [2] categories. The changes from [2] through to the current state of the art are more or less evolutionary the amount of control logic just increasing model by model. At some point the manufacturers change over to a digital controller.

It does indeed. I think your idea of describing sub-systems would work better for this.

The advantage of the full descriptions at least for the older models is that huge proportion of the older designs are almost identical to each other. Describe one model and you have described 30% of all boilers in use.

[Ed Sirett]

Partial FAQ now online. You are permitted and encouraged to rip the boiler specific parts of this FAQ for use in the wiki and elsewhere,

The safety related stuff may only be taken as a whole and must credit "Silicon" Sam Goldwasser of news://sci.electronics.repair