Non sealed-system combis?

[livingstoned]

Are there any combis for about 35kW HW which aren't sealed?
I have to get a boiler replaced where I'm not confident the pipework wouldn't weep at 3+ bar.
(I know there's a compression joint under a tiled floor, and I remember the pipe up to the towel rail rotating in it, in the past.)


I'm aware a second heat exchanger can be used, but that's a layer of complication I'd prefer to avoid if possible.

 

[CountryFan]

None I’m aware of. Why a combi? Intergas Eco RF 30 might suit you, depends on what you’re trying to achieve

 

[livingstoned]

Trying to achieve some heatth

Well, it's a Y plan with a Netaheat IIF 10/16. The pump has failed, after 42 years.
I'm considering options. The boiler could stay until Summer - decisions to be made.

I have a set of spares for the boiler but it's had its day, like me.
Lack of access means the cylinder has to come out unless I can find a plumber with long arms and strong fingers.
It can only be reached to split the nuts really.
A magnet on a stick clamps itself to many of the pipes in the airing cupd so I imagine they're full of crud.
The pipe-up is unconventional, it did splutter in the loft when the pump was set too high.

Only 2 people so a combi would do.
It's on a 15mm gas pipe so work there too.
No easy/quick fix, I think..

 

[CountryFan]

Is there a way to reroute the cylinder, or perhaps make it accessible?

 

[Madrab]

Why not pressure test the system? Get someone that has the tools to run a test and then you'll know if it can take it or not.

Also do remember that the system doesn't need to take 3 bar, that would only be in a fail condition, whereby either the EV had failed or the PRV failed to lift. Most tests would be run @ 1.5 times the working pressure, so you would look to test the system @ around 2.5bar. Of course the system could be run up higher to stress test the components.

I would always pressure test a system going from OV to sealed.

 

[fixitflav]

Are there any combis for about 35kW HW which aren't sealed?

A combi (or system boiler) has a pressure switch to stop it if the pressure drops too low, indicating a need to re-pressurise. If your house is typical, with boiler on the ground floor and F/E tank in the loft, the pressure at the boiler is 0.5 - 0.6 bar. If that is above the pressure switch setting (which might be adjustable) you can pipe the cold feed to the boiler return. The boiler supplier should be able to confirm.

 

[fixitflav]

Well, it's a Y plan with a Netaheat IIF 10/16. The pump has failed, after 42 years.
I'm considering options. The boiler could stay until Summer - decisions to be made.

Does the HW cylinder need replacing? If not you could just replace the boiler and pump. And change the pipe layout, cold feed to the pump discharge as shown is a bad idea. As you suggest, a combi is also likely to need the gas pipe upsizing.

 

[livingstoned]

Is there a way to reroute the cylinder, or perhaps make it accessible?

The cyl is in the way of doing anything. It's in a tight brick airing cupboard. The pump could go higher up the wall, once removed. The idiot who put it in in the first place could have done that. Hey ho.
See? Yes that's a pump spanner but it won't go on a nut:

wrong angle.

Why not pressure test the system? Get someone that has the tools to run a test and then you'll know if it can take it or not.

Because I didn't think of it - far too obvious!.

I could use the mains, cap off the F&E/Vs and let the pressure go up slowly using the trapped air. Our mains is about 3 bar. I have one of those 50bar things somewhere lost but 3 bar should do?? Does anyone use Leak sealer as a precaution or is it verboten, for blocking heat exchangers, now?

Also do remember that the system doesn't need to take 3 bar, that would only be in a fail condition, whereby either the EV had failed or the PRV failed to lift. Most tests would be run @ 1.5 times the working pressure, so you would look to test the system @ around 2.5bar. Of course the system could be run up higher to stress test the components.

I would always pressure test a system going from OV to sealed.

Does the HW cylinder need replacing? If not you could just replace the boiler and pump. And change the pipe layout, cold feed to the pump discharge as shown is a bad idea. As you suggest, a combi is also likely to need the gas pipe upsizing.

Not really. It was a "British Standard" rather than "medium duty" in its day so it heats up quickly, though it isn't up to latest BR. It feeds a 4.5bar ST Monsoon, which is overkill. Bath fills quick though!

The pump went in the return to run cooler. 42 years isn't a bad run, I think. I know the idea that the system could be under negative pressure and have the potential of microleaks, but I have no way to know.

When I was introduced to combis they ran a couple of years between breakdowns - are they better now?
,

 

[flameport]

. It feeds a 4.5bar ST Monsoon, which is overkill. Bath fills quick though!

If you intend to keep the bath, a combi will be severely disappointing after using that pump with a HW cylinder.

 

[dilalio]

Intergas will run on really low pressure.
Down to about 0.5bar IIRC.

Have also come across a few worcestors with no pressure on gauge but still chugging away with no problems reported by tenant/user.

 

[Madrab]

I could use the mains, cap off the F&E/Vs and let the pressure go up slowly using the trapped air. Our mains is about 3 bar. I have one of those 50bar things somewhere lost but 3 bar should do?? Does anyone use Leak sealer as a precaution or is it verboten, for blocking heat exchangers, now?

Yes - absolutely, 3bar would be fine if your mains has the pressure, always bleed as much air as poss though, to provide a true test. leave it overnight if possible. a small fluctuation in pressure is fine, more than say 0.2bar and you're looking for leaks

Leak sealer is an absolutely no no as it can't really be undone and even then it has to be used specific conditions, something I actually learned from a Youtube car channel.

When I was introduced to combis they ran a couple of years between breakdowns - are they better now?

Not really IMO - all but one of the manufacturers have multiple components, 2 HEX's, lots of moving parts etc. That being said most modern boilers, looked after, can run faultless for years.

If you have 3 bar and if the flow is good then an unvented cylinder may be worth considering, gets rid of the pump too.

 

[fixitflav]

Yes - absolutely, 3bar would be fine if your mains has the pressure, always bleed as much air as poss though, to provide a true test. leave it overnight if possible. a small fluctuation in pressure is fine, more than say 0.2bar and you're looking for leaks

The way I see it, the problem with doing a pressure test is what to do if it shows a leak, and it's somewhere not visible and fixable. Can you go back to open vented, and hope it doesn't leak at that pressure (and the test hasn't made it worse)?

 

[Madrab]

The way I see it, the problem with doing a pressure test is what to do if it shows a leak, and it's somewhere not visible and fixable. Can you go back to open vented, and hope it doesn't leak at that pressure (and the test hasn't made it worse)?

Fair point but If I think about it logically then if that was the case then it was probably a leak just waiting to happen and better to show it when the systems is being worked on with all the relative repair resources being available.

I must be honest though and say that I have found it rare that an OV system leaked out on the main part of the system when it was put under pressure. Invariably it leaks at the compression points where the pump/zone valves, rad valves, @ the boiler connections etc and most if not all of them are accessible.

I think I've only eve comes across 2 in all my time when it didn't hold pressure where it was out on the system under floors, one was at a badly corroded soldered joint where it obviously hadn't been cleaned properly and the other where the fitting had been damaged at a notch under a floorboard. It also comes back to the old adage of never using compression anywhere it can't be got at.

Of course I'm not saying it can't happen which I guess is why most pro's will always caveat going from OV to sealed against it leaking, where not of of the system is accessible

 

[muggles]

Intergas Rapid & ECO RF ranges can both be run open vented. Navien can be persuaded to through the installer setup menu if you're familiar with them

 

[Harry Bloomfield]

The cyl is in the way of doing anything. It's in a tight brick airing cupboard. The pump could go higher up the wall, once removed. The idiot who put it in in the first place could have done that. Hey ho.

My airing cupboard, includes a removable timber panel, to allow access - could you do something similar?