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Which is the best: System or Combi Boiler?


macmac
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I would welcome some feedback on Combi Boilers.

There’s seems to be a long standing debate that some say the heating goes cool when the hot water is running.

Especially when you run a bath, or if you had a shower run off the combi.

 

It’s seems that you have to have a boiler with the right LPS (hot water litres per second)
but then to get that it seems you need a much more powerful heating as well?

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Yes a combi sops heating the heating when it is heating water. Inmost houses you would not even notice that has happened.

 

Personally I am not a fan of a combi boiler but I do like a good shower, and I have been in enough houses with a poor combi boiler where the shower goes cold if someone else turns a hot tap on.

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2 hours ago, ProDave said:

Personally I am not a fan of a combi boiler but I do like a good shower, and I have been in enough houses with a poor combi boiler where the shower goes cold if someone else turns a hot tap on.

 

 

In addition to this problem, when showing with a combi there is the mid shower heating overrun/cold/heat restart problem. If the shower is stopped while washing hair the boiler overruns for a few seconds and super heats the now static water before it shuts off. When the shower is restarted the user risks a short slug of scalding water, followed by a few seconds of ice cold water before the heating cycle of the boiler catches up and delivers a fresh stream of hot water to regulated temperature. 

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I have a Combi and very good water pressure - if someone flushes the toilet, I get a small decrease in flow (which does not marr the showering experience) but no noticeable temperature variation at all.

 

Shower is a Grohe 1000, Boiler is Vaillant Ecotec 831+

 

 

Edited by wozza
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If you've got decent water pressure and a smallish house or flat then combi's are great because they only heat the water you use so no storage losses and they never run out of hot water, plus you save tank space. Oversize the lps to avoid issues with pressure dropping when you turn on the hot tap... We never had issues with a decent shower but they take much longer to run a bath. 

 

Bigger houses, then a system boiler is better

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Like @wozza I've not had the problem others discuss. My plumber always likes to oversize the boiler though. I thought showers can go down to about 6l per min now?

Also in new place with the manifold setup I find the water pressure drop is much less of an issue. Ie if flush loo while running basin it is barely noticeable whereas in houses where they share one 15mm supply the tap often slows. 

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Hate combi's with a passion... they are becoming very complex to meet the emissions/energy ratings and your biggest problem is that if you lose the combi you have lost heating and hot water. With a system boiler with tank, more than likely you have immersion backup.

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