Love or Hate your Combi Boiler?

no1catman

Previous (end of terrace) house, had the traditional boiler replaced -2003 by a combi (but it wasn't a condensing one). It had a bath - no problem, and unlike with the hot water tank, if someone else wanted a bath afterwards - no problem, no need to wait hours for the water to heat up.

New house (semi), replaced boiler bizarrely sited over the gas cooker in the kitchen, used the same C/H engineer - who this time advised a condenser combi - only have power shower. Curiously, this used to be prone to sudden cool water, when another tap was in use, but since the old shower unit was replaced hardly notice now.
Still, hot water comes through quickly, and the temperature setting at the boiler can be adjusted.

DominicH

Alex1983 wrote: »

a combi increases the temperature by a set amount usually about 35-40 degrees but will vary from boiler to boiler. So if your cold water is coming in at 5 deg then you will get around 45 deg hot water. The flow rate also affects the temperature of the water.
The hot water tank option will give you the same temperature water all year round as it's stored hot water but you will need to heat the tank up everyday.

Surely the hot water temperature will depend on whatever you've set it to on the control panel? Yes, a less powerful combi may struggle in winter to raise the temperature of cold water to your desired temperature, and so the flow rate may drop, but not because the combi is refusing to raise the temperature by more than a set amount.

Annie1960

I had a combi fitted in my last house and loved it.

I considered getting an unvented system in my current house, but when I looked into it the advantage of an unvented system is that it is good if you have 3 or more bathrooms.

If you go for a combi, I think it would be a good idea to also have an electric shower as a back-up.

Alex1983

DominicH wrote: »

Surely the hot water temperature will depend on whatever you've set it to on the control panel? Yes, a less powerful combi may struggle in winter to raise the temperature of cold water to your desired temperature, and so the flow rate may drop, but not because the combi is refusing to raise the temperature by more than a set amount.

All combis increase cold water main by a set figure at a specific flow rate.

I fitted a 300 litre gledhill that recovered from cold in 29 mins. A lot of modern unventeds around 200 litres recover from cold in around 20mins when connected to a correctly sized boiler

d0nkeyk0ng

We had a hot water cylinder in our parents' house. I don't recall much about because we were quite young then. They upgraded to a vaillant that lasted around 22-23 years. I don't recall it ever being serviced. When that broke down, I replaced it with another vaillant - the same model as your first choice - 832. Parental home a terraced house but each of the three bedrooms are double sized. Total of 9 rads, 3 sinks, 2 toilets, 1 bathtub and 1 shower. No problems with heating or hot water.

Our marital home has a combi too but an electric shower. The pressure and temperature aren't that great compared to a mixed shower fed by combi but because it had a cold water feed only, it would work fine even if the boiler were to break down.

I would love to have a power shower but have been told this has to be via hot water cylinder system as a combi cannot supply water fast enough.

thescouselander

Our combi is great. We've got a Worcester 36CDI which can heat the water as fast as it comes into the house at any time of year.

We considered going for an unvented cylinder instead but they do need a bit of extra maintenance and finding a heating engineer with the correct certificates for unvented systems can be problematic.

[Deleted User]

coffeehound wrote: »

Blimey, what exploded exactly?

Fortunately it used to reach the melting point of solder before the pressure was sufficient to rupture the heat exchanger, so it usually failed by slipping one of the joints. Nevertheless, it was still a big bang followed by a kitchen full of scalding steam then a flood of water.

When the problem first started there was no non-return valve on the rising main, so the pressure could never exceed mains pressure. In those days if the gas valve jammed you could hear knocking in the pipes as the water boiled, and save an explosion by quickly turning the water tap back on while you go and shut off the gas. (Remembering to stand back as the steam and solder droplets come out of the hot tap.)

After the water main was renewed with a non-return valve on it things were very different. There was no way for the pressure to vent back into the main, so failure was almost instant, with no more than a second or two warning. That's when the explosions started.

It took about sixteen years to get the gas board to fix it. At first they sold us a new water heater on the pretext that would solve it, but that was just the same from the day it was new. Repair men used to keep coming round and unjamming the valve, but then shrug their shoulders as if it was all a big puzzle and they'd never seen a problem like it before.

It turns out that there was a modification available to fix it, but nobody told me until they hurriedly fitted it two days after I wrote a letter threatening legal action. That was over 20 years ago now, and it's been fine ever since.

Kernel_Sanders

Nobody seems to have mentioned the Achilles' Heel that unvented systems have; namely, what happens when the water is turned off by the supplier? Whether that be for repairs in the street, contamination or the overdue 1976-style drought, you'll be able to flush your toilet just the once, have no hot water to wash your hands afterwards and no cold even to heat some.

prosaver

a plumber told me combi dont last as long as the other, too many parts or something

fezster

Kernel_Sanders wrote: »

Nobody seems to have mentioned the Achilles' Heel that unvented systems have; namely, what happens when the water is turned off by the supplier? Whether that be for repairs in the street, contamination or the overdue 1976-style drought, you'll be able to flush your toilet just the once, have no hot water to wash your hands afterwards and no cold to even make a cup of tea.

Same for a combi. Only a cold water tank or an accumulator setup would overcome this, neither of which are being considered by the OP.

A combi will run one shower at most. And this will be affected by the opening of another hot outlet simultaneously (i.e. the shower may go cold). You can get bigger combi's to try and overcome this, but no combi will run 2 decent showers all year round. You have to offset this against the convenience of hot water on demand.

Having had an unvented setup, I'd definitely prefer that, unless space prohibited me from having one. You do need to make sure your incoming water supply is sufficient though (this applies to combis also). For unvented, you typically require a 20 l/m flow rate and 1.5 bar dynamic (working) pressure, as a minimum.