Boiler size & cost

BohemianRhapsody

Yes generally happy with the performance of my existing boiler. I think 30kW sounds like the way forward. Not sure about EcoFIT versus EcoTec 'Plus' yet. If anyone has an opinion please do share. I am still considering to let the engineer change the pressure valve and see how that goes. Might be worth the £120, and give us a bit more time to decide on what boiler to get. 

Jeepers_Creepers

BohemianRhapsody said:

daveyjp said:

20l a minute is excellent, certainly enough for a 30-35kw boiler.  Test it yourself.  Turn a tap on full (usually kitchen) and time how long it takes to fill a 1 litre container.
Vaillant do a 38kw combi which is good for 16l of hot water a minute.

Thanks, will did test it, and it looked like 14-15l a minute. I did it in the kitchen, he did it in the garden tap. So I think 35kw probably the max capacity. 

20lpm is nicely solid. ~15lpm is 'fine'. Anything less could be an issue.

It's not only the boiler's flow you need to cater for, but also a cold supply at the same time. For example, if you are having a shower and the boiler is happily delivering its full quota of hot water at, say, 13lpm, bear in mind that this will need mixing with cold water at the shower unless you like having your skin removed. The hot water will be delivered at 60oCor above, so you'll need a good few litres of cold blending in to bring that to a non-lethal ~40oC. So a 15lpm mains supply is suddenly sounding a bit borderline. 

Mind you, if the guy measured 20lpm at the garden tap (also a good place - 'cos the kitchen tap might be restricted by its design), then you are good for a 35kW boiler.

All things considered, tho' - you are happy with your existing 30kW performance (which will almost certainly be noticeably bettered by the more efficient newer model), you plan to make it a system boiler later on, you know your cold supply is fine for a 30kW jobbie, and you know the gas supply is ditto, then I think I would recommend you stick with the '30'.

Do not tho', please, go for less.

For anyone else, I'd say go 'large' :-)

I'd drop Vaillant an email and ask them (a) what's the difference betwixt the two ranges, and (b) is one more suitable than the other for use as a system boiler later on?

fezster

Just be careful, as a loss of pressure could be on your system pipework - changing the boiler wouldn't solve that.

If you are installing an unvented cylinder (don't get a megaflo), then it seems pointless spending extra on a combi boiler. They are more expensive to buy and to maintain than a heat-only or system boiler. If the system does need cleaning, it may be worth trying some Sentinel X400 for a few weeks and see if that clears things up. Also consider that with an unvented cylinder, provided your pressure/flow rate are adequate, you will want 22mm pipework - particularly to your showers.

BohemianRhapsody

Jeepers_Creepers - thanks again, I dropped them an email so will report back if I receive a reply. 
fezster - thanks, yes you are right, the engineer mentioned this as a second potential cause for the dropping pressure, first being issues with the pressure valve. What would the Sentinel X400 do? Would it discover the potential leak on the system? Or just clear the boiler and the pipes? How much would that cost approximately? 

fezster

Sentinel X400 is a system cleaner. You can leave it running in your system for a number of weeks to dislodge the magnetite build up. Ideally, you would have a magetic filter to collect the debris and clean it out multiple times whilst the system is dosed. It's not as good as a full powerflush but it is a relatively cheap way to clean an existing system. I think a 1L bottle is approx £20.

Jeepers_Creepers

BohemianRhapsody said:

fezster said:

What's wrong with your current boiler? Has it broken down and uneconomical to repair?

8 weeks ago it started loosing pressure. I need to increase it every week or so. Also, it's what they call 'cycling', i.e. it gets to a certain temperature and then goes down to protect itself from overheating. Apparently something to do with dirt in the boiler. They couldn't service it because of that as couldn't measure the gas flow I think.  One gas engineer recommended us changing the pressure valve (cost ca £120 including the part) and see if this sorts out the pressure issue, but he said that it could also be a leak on the system. He thinks that if fixed, the boiler could get us through another year or 2 until we have the utility room ready so we can then install directly the Megaflow system, saving money. I am hesitant as keep throwing money on an old boiler doesn't make sense but on the other hand, it might be worth trying. 

Just looking through this thread again, BR, Fez makes a good point.

I'm guessing your plumber has carried out a few checks to see where the leak is coming from, but if he's just speculating that a new pressure release valve could fix it, then perhaps he hasn't...

Do you know what this part is, what it does, and - more importantly - how to check it? Let's cut to the last part - how to check it. Ok, got a pencil and paper? Cool. Put it down. Go outside your house and look at the wall outside where the boiler is located. Look for a 15mm copper pipe coming through the wall somewhere. It'll either be at the boiler height in which case the end will be curved back on itself and be pointing at the wall, or it'll be near the ground, in which case it'll be pointing downwards ideally into a drain. Have you found it? Is the end wet?

If in doubt, place a small plastic bag over the end with a rubber band - see if any water appears as your system pressure drops.

If you can, wait until your utility room is sorted and then go straight for a system boiler. That'll make far more sense - cheaper, smaller, more reliable.

Oh, and if your system has sludge in it, then it might be best to start getting rid of this as soon as you can. Is there a magnetic filter on your system? If so, add system cleaner such as Sentinel X400 and leave it in for a good month or so, checking the filter every few days. When you do come to fit a new boiler, you really want your pipes and rads to be as clean as possible. The clean that'll be (should be) carried out by the installer at the time might not get really compacted sludge.

BohemianRhapsody

Ok so our boiler just made a big bang, the heating was on but the pressure was not down. The body of the boiler actually moved a bit and I had to push it back. Any idea what normally causes this loud bang? We have heard a smaller bangs before, normally when it starts, but this was a much louder one as we actually heard it on the ground floor from the second floor. Could it be the pressure valve or something else? I will try to get in one of the engineers tomorrow to have a look or at least speak to them for advise, but in the meantime would appreciate any views. Thanks.

jefaz07

BohemianRhapsody said:

Ok so our boiler just made a big bang, the heating was on but the pressure was not down. The body of the boiler actually moved a bit and I had to push it back. Any idea what normally causes this loud bang? We have heard a smaller bangs before, normally when it starts, but this was a much louder one as we actually heard it on the ground floor from the second floor. Could it be the pressure valve or something else? I will try to get in one of the engineers tomorrow to have a look or at least speak to them for advise, but in the meantime would appreciate any views. Thanks.

Sounds like explosive ignition. I get it most on Baxi/Potterton boilers. 

Not an expensive fix but get a fitter in. 

BohemianRhapsody

Thanks. Ours is Vaillant TurboMax plus. Maybe 15 years old.