Replacing boiler from a vented to a sealed system.

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miketurner

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I currently have a Glow Worm Flexicom 24hx condensing boiler (13 years old) on the ground floor and a water tank and vented expansion tank in the loft.

My home is a detached chalet style bungalow, ground floor and first floor with a small loft area above. It has 4 bedrooms with around 15 radiators and water under floor heating in the lounge. Three showers and no bath. The house was refurbished and new copper pipe heating/hot water system installed around the year 2000.

I’m aiming to have my boiler replaced and water tanks removed.

My plumber has suggest a Heat Only Ideal boiler, which means fewer pipe runs (otherwise he said he may have to remove walls/floors etc). With a Gledhill hot water cylinder and two expansion vessels in the first floor cupboard. Which is all fine, my only concern is there could be a risk of leaks as the pressure in the pipes will be more than they are at the moment.

Is this a very common risk and is there some way I can calculate this.

Also I’m thinking of getting an Ideal boiler with a Kw output of 30 instead of the 24kw existing one as sometimes one of our radiators at the end of the system does not seem to get very warm.

Our current system has a shower pump fitted so all showers can be run at the same time without noticing much difference. Our plumber mentioned that he would remove the shower pump and we might not be able to run two showers at the same time, or if we did we would notice the difference in pressure. Maybe I could ask him to keep the existing shower pump ?

Also does anyone have any experience of the Ideal Halo wireless thermostat ? (similar to Nest/Hive.)

Any advice appreciated, thanks.
 
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Firstly, your engineer needs to look at the dynamic pressure and flow of your cold water mains to establish whether an unvented hot water cylinder is suitable to be used (make sure he's qualified to install unvented by seeing his ticket). If the dynamic pressure and flow is suitable to supply an unvented cylinder properly then you should be able to supply multiple showers with minimal impact to overall output.

If changing from open vent to sealed then he should pressure test your system before converting to ensure it is sound and can take the pressure but even then there is always a caveat when changing a system over, that some fittings may leak longer term, nothing that can be done about it unfortunately.
 
miketurner said:
Also I’m thinking of getting an Ideal boiler with a Kw output of 30 instead of the 24kw existing one as sometimes one of our radiators at the end of the system does not seem to get very warm.
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Radiators not heating is caused by poor circulation, which can be due to various things such as a blockage, system not balanced or incorrect pipework design.
Shoving in a larger boiler will not help that at all, and unless your property is massive, a 30kW boiler is grossly oversized.

The heat output of the boiler needs to be sized to the heat requirements of the building, otherwise it either won't heat the property effectively or will be inefficient due to it being too powerful.
 
Ok thanks, I think the system was not balanced as I had previously tried to change the balance on some radiators. Perhaps the 24kw model (same as my existing one) might be more suitable, assuming it will be more efficient. I will ask the plumber when he next visits. He is not available to fit for some 4-5 months but I’m doing some preparation first. Thanks again.
 
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miketurner said:
Ok thanks. So perhaps the 24kw model (same as my existing one) might be more suitable, assuming it will be more efficient. I will ask the plumber when he next visits. He is not available to fit for some 4-5 months but I’m doing some preparation first. Thanks again.
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If you are going heat only with stored hot water, I don’t think you'd need any more than 24kw. probably less. Get a heating engineer to do a proper heat loss calculation.
 
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Hi, Madrab, Thanks for the info I will get him to check the dynamic pressure and pressure test. Do you know what the range should be for it to be suitable for an unvented system and what the range for the pressure test might be ?
 
I can run 3 hi flow showers, 2 en suite and 1 main at the same time on a 250L Unvented with a 4bar dynamic @ 28L/min mains supply. Yes you do notice a little drop off in perfomance when all three are on as the UV is limited to 3 bar but that's only because I fitted them and I know what to look for, wouldn't notice normally I wouldn't think.

You don't want any less than 3 bar dynamic @ 25L/Min if you are running 3 at the same time.

Have to agree about the boiler rating, I recently installed a 24Kw sys boiler into a largish house with 16 rads over a larger footprint property, it's more than enough to cater for the requirement. It does need a nice clean system that's finely balanced, as any larger installation does.
 
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miketurner said:
Also I’m thinking of getting an Ideal boiler with a Kw output of 30 instead of the 24kw existing one as sometimes one of our radiators at the end of the system does not seem to get very warm.
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You need to get a proper room-by-room heat loss calculation done (or do one yourself) rather than just guessing. A higher power boiler might actually make the problem worse. It sounds like you may have a circulation issue rather than a power issue.

www.heat-engineer.com will give you a very accurate heat loss calculation if you spend the £12 for the full survey and a couple of hours going around your home to complete it.
 
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