Combi or Standard Boiler?

[gerbils]

We have a Glow Worm Space Saver mkII which is over 30 years old...

It's obviously incredibly inefficient but is working fine... we know eventually this will break and so wondering if we should invest in a new boiler now to save monthly costs now energy prices are through the roof.

The question is, do we get a combi or stick with a standard boiler?

4 bed detached, 4 occupants, 2 showers, 11 radiators.

I am unsure how often we'd run 2 showers at once, but as I understand it, this as the only drawback to a combi?

Benefits would be

1) Better water pressure vs our pathetic gravity stsem
2) Space saving in cupboard and roof

Any opinions?

 

[Mottie]

We had our system converted to a sealed system and unvented hot water, getting rid of the tanks in the loft and getting a mains pressure shower, keeping the original heat only boiler. We had a digital room stat and programmer fitted at the same time. When the boiler packed up we just replaced the boiler with another heat only one.

 

[ericmark]

The system boiler allows you to all energy from other sources, like solar panels, and the boiler can be smaller and still have enough DHW for a bath or shower, using a power shower the shower is far better using a system boiler, and the boiler can be switched off in summer months and an immersion heater can give you DHW.

The combi boiler either has a reservoir inside, so really a system boiler, or it has a delay from turn on to getting hot water to the taps, to gain the advantages you often need smaller bore pipes to old system boiler, as bigger pipes mean more water needs to be run before getting hot water. It does deliver DHW at mains pressure, so no need for a pressured tank or power shower, but it can't produce enough hot water for side jets on the shower, or fill a bath anywhere near as fast as a system boiler. It also means unless a small radiator is fitted into airing cupboard it no longer gets warm, although to be fair modern tanks are very well insulated so airing cupboards don't get that warm anyway.

If not using Eco setting a combi can get shower hot then cold then hot again, as it uses up the small amount of water in the reservoir before the boiler is up to temp, so there is a short cold bit.

However if the combi is fitted near the point of main use, i.e. in the kitchen, it can reduce the delay on hot water, and it does save space.

To my mind the combi boiler is often a cheat, at least with oil, it still has a reservoir, but built into the boiler, not tried a shower with an oil combi, not sure if it runs out of water, with a gas combi it does not need to have a reservoir it can modulate (turn down) so a true instant heat, but if the boiler fails there is no electric back up.

I have a system boiler (oil) but for some unknown reason two electric instant showers, with a shower on top floor, yes the pressure is low without it being a power shower, but one of mine on middle floor and the other on lower floor, so there would have been loads of pressure.

 

[oldbutnotdead]

Check your mains cold water flow (and ideally dynamic pressure) before deciding either combi or unvented cylinder. Remember a cylinder gives you options on how you heat your water...

 

[gerbils]

Check your mains cold water flow (and ideally dynamic pressure) before deciding either combi or unvented cylinder. Remember a cylinder gives you options on how you heat your water...

I can fill 1liter from the bathroom tap in around 5.5 seconds. No idea if that's good or bad.

Our shower is pretty pathetic.

Edit: Just noticed we have one of these: https://www.anchorpumps.com/grundfos-ups-15-60-130-super-selectric-domestic-heating-circulator-240v

Is that pumping the heating or the shower?

 

[bernardgreen]

We are having new gas mains in the village, people with gas combi boilers may have no means of heating water ( other than a kettle ) while their gas service is not available. Those with a hot water cylinder probably have the option of heating by electric immersion heater.

CBFF - Overview and History of Combination Boilers

www.thnet.co.uk

 

[gerbils]

We are having new gas mains in the village, people with gas combi boilers may have no means of heating water ( other than a kettle ) while their gas service is not available. Those with a hot water cylinder probably have the option of heating by electric immersion heater.

CBFF - Overview and History of Combination Boilers

www.thnet.co.uk

Thanks, yes that is a benefit I hadn't considered.

 

[Mottie]

It’s not just loss of gas. With a combi, if it packs up for any reason, you’ll have no heating or hot water. With stored water, you can usually at least have hot water with no heating.

 

[Harry Bloomfield]

Your installer will want for various reasons to persuade you to convert to a combi. A gravity system already installed, has many benefits and would cost you a lot more than a combi to install, if you were starting from scratch. If what you have is in good condition - keep it, just replace the boiler.

Despite modern boilers being able to modulate, a gravity system (depending on how you use it) has potential to be run more efficiently than a combi. As above, you may also have the benefit of an immersion heater with a gravity system, should the boiler fail.

 

[vulcancontinental]

I recommend getting

Thanks, yes that is a benefit I hadn't considered.

Get an electric shower and an electric fan heater if a combi or the fan heater alone if a system boiler and cylinder with immersion heater; sorted

 

[vulcancontinental]

Despite modern boilers being able to modulate, a gravity system (depending on how you use it) has potential to be run more efficiently than a combi. As above, you may also have the benefit of an immersion heater with a gravity system, should the boiler fail.

Do you have any independent data to back that, at first reading, ludicrous statement up?

 

[oldbutnotdead]

I can fill 1liter from the bathroom tap in around 5.5 seconds. No idea if that's good or bad.

Our shower is pretty pathetic.

Edit: Just noticed we have one of these: https://www.anchorpumps.com/grundfos-ups-15-60-130-super-selectric-domestic-heating-circulator-240v

Is that pumping the heating or the shower?

The bath tap isn't a reliable guide (it may be running from a tank). Kitchen sink tap should be mains fed and is usually nearest the water pipe entry into the house, do your bucket experiment there (method I use is fill bucket at full bore for 30 seconds then measure bucket contents and double for litres per minute. Pressure needs a gauge to measure.
12 l/min at the bath tap (roughly what you've got) isn't impressive...
Your pump is circulating water within the radiators, nowt to do with hot water.
Many installers (especially the nationals) will try and push a combi on you.
Yes a more modern boiler will extract more useful energy per cubic metre of gas but a straight boiler swap will cost £1600 plus, it'll take a while to recover that solely from boiler efficiency gains, longer if your existing boiler is regularly serviced and maintained. Older boilers have very few moving parts, much less on them to fail.

 

[gerbils]

Your installer will want for various reasons to persuade you to convert to a combi. A gravity system already installed, has many benefits and would cost you a lot more than a combi to install, if you were starting from scratch. If what you have is in good condition - keep it, just replace the boiler.

Despite modern boilers being able to modulate, a gravity system (depending on how you use it) has potential to be run more efficiently than a combi. As above, you may also have the benefit of an immersion heater with a gravity system, should the boiler fail.

Thanks, yes I am finding everyone wants to do a combi with seems at odds with online advice.

Why would this be?

If we stuck with a standard boiler, would there be any point/benefit in replacing the tank? We have a 30+ year old beast with no kind of insulation like they have now.

 

[gerbils]

The bath tap isn't a reliable guide (it may be running from a tank). Kitchen sink tap should be mains fed and is usually nearest the water pipe entry into the house, do your bucket experiment there (method I use is fill bucket at full bore for 30 seconds then measure bucket contents and double for litres per minute. Pressure needs a gauge to measure.
12 l/min at the bath tap (roughly what you've got) isn't impressive...
Your pump is circulating water within the radiators, nowt to do with hot water.
Many installers (especially the nationals) will try and push a combi on you.
Yes a more modern boiler will extract more useful energy per cubic metre of gas but a straight boiler swap will cost £1600 plus, it'll take a while to recover that solely from boiler efficiency gains, longer if your existing boiler is regularly serviced and maintained. Older boilers have very few moving parts, much less on them to fail.

Thank you. The 12 l/min was actually the kitchen tap, my mistake.

Quotes for a standard boiler swap are around £2500, so with a possible £500 a year saving this would take 5+ years to make sense - I get what you're saying.

If we went for a shower pump only for the time being, I am guessing this would be compatible with any future boiler replacement so long as it was. standard boiler..?

 

[oldbutnotdead]

Thanks, yes I am finding everyone wants to do a combi with seems at odds with online advice.

Why would this be?

If we stuck with a standard boiler, would there be any point/benefit in replacing the tank? We have a 30+ year old beast with no kind of insulation like they have now.

Is that the hot water cylinder has zero insulation? Not sure about pricing on them this year but almost certainly worth looking at one with solid insulation, that will pay back very quickly.
If it's the header tank or f & e tank not insulated, buy some loose jackets (so they don't freeze in the winter)
If your water flow/pressure is up to it (ask your water supplier to test flow/pressure) an unvented cylinder might be an option.