i need to do something about our shower its heated by the multipoint boiler and is passable in summertime but come winter and it cant heat a reasonable flow of water
i was thinking about electric but was put off by comments i read this afternoon suggesting that their performance is also poor,particularly in cold weather
anyone able to offer informed opinion/advice ?
pete
I'd agree that you will find a 6 kW / 25 amp one disappointing at this time of year. IME the higher power ones are better, but you would need an electrician to add a suitable circuit (unless, perhaps, you have an unused cooker circuit). And you might need a new consumer unit.
10Kw electric showers are ok, as long as you have sufficient mains pressure. Usual point about specialised electrical circuit.
Has the boiler always been poor at producing sufficient hot water though? Might need the heat exchanger descaled.
If the boiler heat exchanger needs descaling, the last thing he needs is an electric shower!
A 10 kW electric shower should be able to give more than 4 l/min flow with a 35 degree rise ie 10 C to 45 C. A 7 kW one less than 3 l/min with the same temp rise. Depends what you want from a shower, low volume high pressure needles or high volume low pressure drencher.
10 kW is 43 A, the wise would check what the capacity of the incoming mains supply is. An old installation may only have a 40 A incomer fuse, OK it'll not blow for the 10 minute duration of a shower but it's not good practice.snip
the boiler is serviced each year,it burns cleanly and theres no debris on the outside of the heat exchanger.can it be cleaned internally?
i was considering a 10kw electric heater but i see the gas boiler is rated at 24kw.can i really expect the 10kw electric to perform better?
im now thinking about a hot water tank..im getting tired of this already..
pete
Put an electric shower in series with the hot water feed?
Although that may not constitute sensible advice though!
-Gordon
We don't even know if you live in a hard water area, but if you do then Tim's comment is valid! I'll let other's comment on the practicality of de-scaling DHW heat exchangers, obviously depends on the boiler :)
As for the comparison, since the electric shower will be virtually 100% efficient I guess it depends exactly how efficient the gas boiler is, if it's better than 60% then clearly the boiler would be better...
... want a shower in a kitchen, and also no more than the typical 32A of a cooker circuit ;-)
What is the make and model of the multipoint? or failing that, do you know its output power?
Chances are, a gas multipoint is already more powerful than the most powerful electric shower.
Have a look at:
That gives you expected flow rates for different power heaters.
Have you actually measured the flow rate at the shower with it set to what you find to be an acceptable temperature (use a bucket of known volume and a stopwatch)? Once you know what you are getting, you can make an estimate of what you need.
Does this boiler also run the central heating? (if so, its a "combination boiler" aka "combi", and not a multipoint, which is just an "instant" water heater)?
Most combis have two heat exchangers. The main one that the heating water circulated round - thus heating the rads, and then a secondary plate heat exchanger (PHE) that is used to heat the incoming cold mains water for the taps. They normally include a diversion valve that switches the flow of the main HE from the rads to one side of the PHE. The other side of the PHE in turn heats the water. Its this mains water side of the PHE than can become very scaled, and this will reduce the rate at which it can heat dramatically.
Not a chance, unless its heat exchanger is badly scaled or otherwise compromised.
That would be an option. You would probably need an unvented one if you have a good mains pressure and flow and don't want to use a pump for the shower.
This is the secondary exchanger - plate exchanger. If it used to be better, then this probably needs descaling. I could be wrong, but I can't imagine anyone cleaning the plate exchanger during a service. They will usually just replace it when it completely blocks. If you are DIY'ing it so your time is not being charged, then descaling it is a cheaper option. You'll need a tub of Furnox DS-3 (sulphamic acid), from BES or (more expensive) from a local plumber's merchant. Plate exchangers hold a lot of scale - a kettle descaler sachet won't touch it.
Does sound like the plate exchanger. Did it used to be better?
There might be other issues too: for example, is the bathroom warm enough? If you're in the altogether, even before you get under the shower are you shivering? What about when you step out, wet?
Even if the water comes out of the shower-head reasonably hot, is it falling through too-cold air?
Showers (as other posts mention) tend to be rated in terms of such and such a flow rate for a particular rise in temperature of the water. But in winter, the incoming water might be a lot colder than you think, so the result will be no good.
I must admit I've wondered if there's any way to store incoming water at mains pressure, to take the edge of its coolth.
10kW electrics will give much poorer results than 24kW gas, as long as the latter works ok. Once you've sorted what can be done, there is one last option, an alternative to going stored:
NT
One thing not mentioned so far. If you are in a hard water area your heat exchanger may be furred up. If you clean or replace it will only fur up again. Have you considered a water softener? Over time this should slowly remove the fur from the heat exchanger and you will not have any further problems with furring up.
Just something else to add to your cost/benefit analysis.
Cheers
Dave R
thanks guys for the helpful responses
the boiler is a Main combi 24he rated at 24kw we have lived here for 4 years now and the shower has always been disappointing I understand that the boiler is about ten years old
I just measured the flow rates and temps at the kitchen sink and got
cold flow (cold tap fully open) was 12.2 litres per min and temp 11.5c
opening the hot tap to get 41c gave 3.6 litres per min
looking at Dave Liquorice's temperature rise figures for a 10kw heater suggests this boiler is seriously underperforming ?
pete
My 2p: we are on our second Mira Sport electric shower (first one lasted about a dozen years, second one's about 9 years old now I'd guess).
It's fine for us (two); we don't make massive demands on our shower (don't need power showers, don't stay in longer than 10 minutes).
We have to turn the heat control up *a little bit* in winter, when the water supply is a little cooler, but all in all it's extremely convenient and reliable.
J.
Kind of, its called a cold water accumulator. Typically fitted to improve flow rate on properties with limited feeds
e.g.
They buffer cold water, but are usually insulated to prevent condensation pouring off them.
If you are going to warm the stored water, then you really need an unvented cylinder.
Manual for that model specs 11.5 lpm @30C rise... Just a thought, but how well does this boiler heat the radiators?
Take there is sufficient DHW flow, it's just not heating it enough?
One simple thing to check, if it has a speed switch on the pump (manual suggests not though) make sure it's set to "high". Also, another simple thing to check, when in DHW mode, check whether the CH flow pipe is getting hot, in case the diverter valve is not functioning properly. Also, if you can see the flame (or gas meter) see if it's in full gas rate at maximum DHW water flow. If it's modulating down, it could be that the primary circuit is hot enough and there is insufficient heat transfer to the cold water, ie the plate is badly scaled :)
thanks for the reply Lee.Much appreciated
With the CH set to max the rads are too hot to touch And yes,the DHW flow is sufficient ,it just doesnt get hot I take it you are referring to the Grundfos CH pump in which case i cant see a speed switch
I have now taken the cover off the burner and the burner lights fully for CH but for DHW it lights fully,then after ten seconds or so the flame either goes out ,or reduces in intensity.
So the problem is scaling ? or is there anything else i can check before getting the Furnox? or is a new heat exchanger a sensible option?
cheers
pete
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