condensing boiler advice!

[derekgas]

just a note to people with condensing boilers, the regs say that the white pipe should be lagged if it extends to the outside, or, should be upsized, and this would prevent freezing, we have however, had several calls to boilers not working (around 12), every one had a frozen condense pipe, as it will freexe again tonight, I would advise that you turn the hot water side off, or down (dependent on system) and try not to use hot water late at night, if your boiler does stop working, pour hot water on the pipe outside and reset the boiler, if you wish, you can call an engineer who will charge you to do exactly the same! Keep warm!

[Neil]

I thought you were going to advise people not to fit those damned things that the Government have inflicted on us

[MargaretR]

Originally Posted by Neil

I thought you were going to advise people not to fit those damned things that the Government have inflicted on us

Glad you added
I like mine - 90.2% efficiency at last test

[Neil]

Originally Posted by MargaretR

Glad you added
I like mine - 90.2% efficiency at last test

How exactly did you arrive at those figures?

[MargaretR]

Originally Posted by Neil

How exactly did you arrive at those figures?

The maintenence man from Hyndburn Homes had a gadget to test it and showed me the reading

[panther]

Iv got an condensed boiler, and the only pipe i have outside is that drain pipe and that thingy that dripps every now and then...well it did when i had my old boiler

[MargaretR]

My boiler is in a walk-in type cupboard in the bathroom.
It has a wide exhaust pipe leading to the outside wall and some short gadget on the outside from which steam comes out when I run hot water

[derekgas]

Nei, the gadget is called a flue gas analyzer, I have 4 of them, Jacqui and Margaret, it sounds as though the offending pipe in your case is plumbed internally, so this wont affect you, only people who have a condensate pipe outside.

[Neil]

Originally Posted by derekgas

Neil, the gadget is called a flue gas analyzer, I have 4 of them

Does it not depend when you check them? I was under the impression that testing them from cold will give better results than when the house is nice and warm and the boiler return temps are higher as the condenser will have to do more work.

They are more efficient at certain times but I can never remember which way round it is, its either running flat out making hot water or tickling along running the heating.

Another reason why I don't some of them is they have aluminium condensers. The condensate is very corrosive and slowly eats away the aluminium. The fabricated stainless steel condensers are better but more expensive.

I think in the end my dislike comes from the initial high cost for the boiler and the crazy spare part price - then again that can be true for most combi's

[derekgas]

The ideal test is 10 minutes from cold, but are more often tested when warm, you have non user adjustments to fire them up on high or low regardless of what the boiler would do in normal mode, it is sad to say that most engineers do not know how to test condensing boilers, when I asked the question not too long ago at an 'engineers' meet, most said they serviced in the same way as the old ones, this cant be done, and I was told by one that 'I just hoover the innards like I used to with the old ones' , condensing boilers are more efficient when they are working harder, this is why you cannot just put a boiler in, (regular condensing, with tanks), it has to sized correctly, not oversized as happened previously. Some of these boilers have aluminium heat exchangers, but NOT condensers, the condense comes from the flue which is plastic, and runs through a plastic trap/drain, I have seen them run in copper, which is a poor poor job, worcester bosch have an aluminium heatex, but is gauranteed for 10 years providing that the water quality is correct, again, most dont have the equipment or dont know how to use it properly, and so the water in the system is left acidic/alkaline which will damage an aluminium heatex in 2 - 7 years, aluminium transfers heat better, steel holds the heat better, thats the main difference. The cost for a proper job, with the correct boiler etc isnt cheap, but with a 5 years manufacturers gaurantee, then maintenance contracts at £12.42 per month (with us anyway), it isnt overly important.

[Neil]

I used to cast aluminium condensers for Baxi/Potterton. I am not surprised that some engineers don't know about the new condensing boilers. It is a worry though when you are paying them a lot of money to service/repair them.

The condenser is a part of the flue really. Its job is to scavenge as much heat from the flue gas as possible. This is not a new idea - we had the same on some 1950's coal fired boilers at one place I worked, they were rather larger than domestic ones though . If boiler return temps are high then the condenser itself will be hot and will take little heat out of the flu gasses. If return temps are low then so will be the condenser and it will be able to reclaim more heat from the flue gasses.

I can understand why it is important to correctly size condensing boilers. I think the important thing when selecting a combi is the hot water flow rate. Who want to wait an hour for the bath to fill up? Do condenser boiler modulate the gas flow to the burner relative to water return temps? If so I would have though having an oversized boiler would just run at a lower output but still give a good domestic hot water flow rate.

[derekgas]

The return temp should ideally be around 20 degrees lower than the flow temp, this optimises the secondary heatex, but, as you say, causes more condensation. You misunderstood the part about sizing boilers, the size and control of the hot water is paramount for the hot water, some boilers condense in heating AND hot water modes and other do not, this is important for high hot water usage (more than 2 -3 baths a week), if you do not use enough hot water, then using a boiler which condenses in both modes is not economical, neither is using one that doesnt if you do use a lot of hot water, if you wait an hour for the bath, then it is the wrong boiler for you, they are fully modulating, but have flow rates which are dependent on boiler size, the heating is mostly irrelevent in a normal house, because combis are at least 24kw, and can usually cope easily on the heating side, regular boiler (now pay attention here Neil) are sized from 12kw up to 42kw, these are designed to more suit applications where the hot water needs to run more than one bath simoultaneously for example, or where stored water is a requirement for other reasons, give that some houses may only have 4 radiators, but want a quick filling bath, then a 12kw would be more efficient, as will a 40kw boiler if you have 17 radiators and 2 bathrooms with an ensuite and a 300 litre mains fed cylinder. In summary, combis should be sized, and rated for hot water use, regular boilers should be sized for the heating and the hot water requirements.

[Neil]

What do you think of the baxi/potterton combi's that have the small inbuilt hot water store so you get hot water quicker when you turn the tap on?

[derekgas]

I always classify baxi/potterton/main as middle of the road, and dont use them unless requested to do so by the customer, Worcester have had a small heat store for years, and the new ones time the hot water 'pre-heat' with some boilers providing the right timeclock/programmer is used, if the wrong programmer is used (and sometimes has to be, especially for people who dont like digital) then the preheat can be turned on or off. We have a pricing scale which gives 3 main options:-

Worcester Bosch/Vaillant

Baxi, Ideal, (and other popular British makes)

Biasi, ravenheat, Rehema,(and other popular foreign makes)

We wont use Ferroli, saunier duval, and other italian or french makes, though we do service and repair them.