Boiler advice

Hi,
Sorry, this isn't directly DIY and is probably a little longer than necessary, but I would like to understand how this works before I take the decision on whether to get my boiler repaired or replaced.
I have a Worcester 24i boiler in my house, which is a four bedroom mid-terrace with ten radiators, a bathroom, an en-suite, a kitchen and a laundry room (with sink and washing machine).
Lately the boiler's become unreliable. Sometimes I'll run the hot tap and get nothing but cold water, sometimes the CH wont come on, sometimes when I try to run a bath it'll start hot and then, after a few minutes, the water will run cold. The same thing might happen while I'm doing the washing up and it'll take me a few tries faffing around with the taps and switching the boiler on and off, before I can get the hot water flowing again. I'll look through the peephole and see no fire.
It's a combi boiler, so I assume it should keep heating the water for as long as I require.
A plumber came round earlier today and advised that there were probably three issues: the PCB (relays were chattering as he played with the timer), the clock (clicking noisily as a matter of course and cutting in and out when he pressed on it) and the fan (noisy bearing and possibly not creating sufficient pressure) and that these would cost approx 500+VAT to sort.
He suggested that it wasn't worth the cost of repair as more repairs would be likely to follow down the line due to the age of the boiler, which he put at 7-8 years old.
About 1 year ago, a different plumber visited to rectify another problem: I had complained that the flow of hot water in the upstairs bathroom was too slow. He removed a plastic thing from the boiler which he referred to as the "flow regulator" and this seemed to do the trick.
Today's plumber says that this was illegal insofar as, if the previous plumber were Corgi registered, he would never have made this modification which is against the manufacturer's spec and, therefore illegal and, if he weren't Corgi registered, he shouldn't have touched the boiler in the first place. In removing the plastic flow regulator, my boiler could overheat, catch fire and I would not be insured for any of the damage, because of the illegal removal of the flow-regulator.
His best advise was that the existing boiler isn't sufficient for a house of this size anyway and that removing the flow-regulator was, in effect, a botch to keep me happy, on the cheap. He stated that the boiler delivers 9 litres/minute which isn't enough for a house of this size.
Now I know very little about this sort of stuff and I hate not understanding these things for myself. My unqualified logic would be that the boiler has been big enough for several years and that it should be big enough after the faults have been rectified. But the plumber advises that the flow-regulator removal is proof of the existing boiler's inadequacy - if it had the required capacity, the flow regulator would not have been removed to rectify the slow hot water in the bathroom, in the first place, and having no flow-regulator now is dangerous.
I'd like to add an en-suite shower to the master bedroom soon and would not like to spend on an aging boiler today, only to have to replace it in a few months with a boiler with a greater capacity, in order to accommodate what I hope will include a power-shower and another sink. But I don't want to spend the 1300 quoted for a new boiler+fitting, if I've simply misunderstood the plumber's advise and a repair+service will do the trick.
Please can those of you with experience explain to me whether my concern should be to get the boiler repaired and serviced on the basis that service is required after 7-odd years but the boiler is adequate or whether I should be looking to replace the boiler so as to improve existing hot water service and provide for the future.
Many thanks.
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Sounds to me like your boiler is knackered, you can pick up good reliable boilers such as the Valliant or better still Worcester Bosch 36i model for around 700 plus installation.

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JustMe wrote:

This sounds very odd to me, I'm no expert, but I'll put my tuppence worth in anyway, and hopefully Ed Sirett will be along to put us straight. You only have to be Corgi registered to touch the gas side of the thing, now I assume this flow regulator was in the water side, so in this case he is incorrect about the requirement for Corgi registration. The only purpose I can see for a flow regulator in the water side is if your pressure is high enough that the flow rate through the boiler is larger than it can handle and therefore even on maximum power you don't get an acceptable temperature rise. Removing such a regulator is hardly going to cause the boiler to over heat, in fact increasing the flow rate will help to remove heat more quickly. I'd suggest a different plumber.
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JustMe wrote:

Perhaps it's just me, but I don't think that's old.
Mine has done 21 years with only minor problems.
Andy
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You're clearly not involved in the heating industry then ! Please do try and keep up. ;-)
Andy
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Andy Cap wrote:

No, I'm not. I just like to keep my house warm, and not spend too much. A couple of spares from Geoff (not in the gas circuit!) and it's been fine.
Since I've found out that in order to get the advertised benefits of a condensing boiler I'd have to upgrade my rads to bring the return flow temp down, I've decided I want to keep it going as long as possible!
Andy
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Andy Champ wrote:

not true for the vast bulk of the year... the majority of the time the boiler modulation facility will do this for you just fine. On the very coldest days it may need to up the flow temperature to keep you warm enough - but this will only be true if your rads were minimally sized in the first place.
--
Cheers,

John.

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John Rumm wrote:

I've thought about this for a bit, and I don't get it.
Yes, modulation would help. Not much though. My current boiler short-cycles once the water in the circuit is up to temp., and it would cut that out. But...
In a normal system the only feedback the boiler has is the water temp. and the main thermostat.
As the weather warms up the TRVs would throttle back the rads until the boiler modulates. The returned temp would then be high enough that it isn't pluming, and I wouldn't get the condenser benefits.
How is the boiler going to know that it's a cold day, and it needs to up the flow temperature? Surely it'll heat the water until it's hot, and let the TRVs (or main thermostat) do the clever stuff?
Andy
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The boiler monitors the flow and return temperatures. When they narrow it know the house is up to temp and reduces the flow temp. When it widens it raises the flow temp. If it is clever enough it will also maintain the delta T of the heat exchanger raising or lowering the flow to suit.
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Andy Champ wrote:

Yup, plus external temperature compensation. This comes in two forms - automatic - i.e. snazzy boiler with external temp sensor, and manual - i.e. you notice the house is not getting warm enough on a particularly cold day and tweak up the water temperature stat on the boiler.

The boiler will reduce input power in an attempt to keep the return temperature low enough to still reap some condensing benefit (you will get a benefit from a condensing boiler anyway even when not condensing simply due to its larger / more efficient HE).

In the simplest of setups it won't "know", all it will see is the house takes longer to reach temperature and the return temperature does not climb so fast / high as normal. Heat loss rate for the building will be faster and hence the boiler will either not modulate as low, or will cycle less.

Yup, along with sticking as little heat in as it thinks is required, and extracting as much heat out of the fuel as it possibly can.
--
Cheers,

John.

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On Wed, 20 Feb 2008 00:14:28 +0000, John Rumm

I guess if the rads are poorly balanced (with the lockshield valves too far open) the high return temperature could result in the boiler modulating down "too early"?
M.
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Mark wrote:

Poorly balanced rads may have the effect of reducing the total heating load a little, so yes you may see it begin to modulate when some rooms are still cold. The situation is less dire if you have TRVs since that will compensate for the poor balance to an extent.
--
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John.

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John Rumm wrote:

Ah. Another feature to look for...

I already have this feature :)

So Drivel's right then - the smaller the difference, the lower the output temp? Seems to me it'll take some careful work to avoid positive feedback there. Because if it lowers the output temp. too soon, the house isn't going to get warm at all... and if it takes it up too high, no condensing.
I take your point about it being (a bit) more efficient even when not condensing; however this isn't going to pay for a new unit.
Thanks
Andy
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Andy Champ wrote:

To be fair this is all I had on mine, and never found the need to use it. I just left the temp control sat at "2" (where max was "6")

Depends a bit on how the boiler does its modulation... the simplest control would be to modulate so as to attempt to keep the return below the dew point. The flow will be limited by the max water temp stat.

It can only lower it to the minimum of the modulation range. On some boilers this is still quite high power (i.e. 8kW or more)

Probably not... depends on where you are starting from I guess.
--
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John.

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Couldn't agree more. The trend to more complex boilers, requiring both more detailed maintenance, without doubt suffering from far more costly failures and ridiculously short lives, TOTALLY outweighs any benefits for the end-user, even if there is a marginal environmental gain, I even suspect that is debatable when total resoruces and time are included
Andy C
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wrote:>> Since I've found out that in order

Nope. Modern condensing boilers module the burner down to keep the return temperature as low as possible. The rads are designed for -1C outside. Anything above -1C and the system is on part load and the rads are then too big. A modern condensing boiler will take advanatge of this.
With current fuel prices, it makes sense fitting condensing boiler as the payback is quite short.

Downward firing burner heat exchangers don't require cleaning. The condensate washes down.

The complexity is also in non-condensing boilers too.

Only if you buy crap and have it installed incorrectly. Buy an Atmos and have it installed correctly and have Magnaclean filter on it. That will last and last and they just don't go wrong.
Get what you pay for comes to mind.
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So what exactly is the 80 - 120 for ?

No excuse. ;-)

As a matter of interest how much are you talking about for an Atmos boiler then? Whatever the cost, it will FAR outweigh the four thermo-couples and one new cap my boiler has had in over 20 years. After fitting TRVs last year my gas bill is 32 / month and looks as if it will be enough. How much do I have to save to make fitting the Atmos worthwhile ?
Andy
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On Thu, 14 Feb 2008 07:03:46 +0000, Andy Cap wrote:

I'd disagree. Modern boilers are probably more variable in the range of qualities that are available and they are more sensitive to poor quality. The best however may well last very well.
They don't make them like they used to - thank God! Having struggled to remove a 200kg 70kW monster this morning my apprentice and I almost fell over laughing at the new boiler with the box that said 43kg 2 man lift!
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Andy Cap wrote:

My gas bill is about the same as yours, 36 here for about 12000 kWh a year, into a 28-year-old Glowworm Galaxie back-boiler.
To have it replaced might cost 4000 (I couldn't DIY it, not fit enough), which means I'd lose 4000 x 0.05 = 200 a year in interest on the outlay.
The flash new boiler would have to save approaching 50 percent of gas usage to cover this loss; and I've never seen that claimed even by the most ardent proponent of condensing boilers.
But, when you look into it, the figure usually quoted is 'boiler' efficiency, not 'system' efficiency. Add in the overflow radiator, airing-cupboard radiator, cycling just to keep a couple of litres of water hot in case you need it, run the hot water for a shower and it goes cold-hot-cold-hot before steadying down, and I suspect the 'system' efficiency is rather less than claimed, making payback very much longer.
And it won't save the planet either. Earth's climate is controlled through sunspot activity. We haven't found a way to control the sun, so unplugging your mobile phone charger (half page government ad in the Sunday papers last year) or paying big bucks to change your boiler won't help either.
Stick with what you've got.....
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wrote:

Ah, the voice of reason. I agree about saving the planet too. The world's population needs to be about halved, if the present standard of living is to become universal. Using condensing boilers and not using plastic bags wont cut it.
Andy
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