Oil boilers, combi or not?

[dobbslc]

I'll be replacing the 40 year old oil boiler at home soon and I'm not sure weather to go for a combi or a system boiler.
I'm replacing the whole system throughout the house (all pipes radiators etc) as it's constantly failing through old age and poor installation. It's an old single pipe layout with no insulation anywhere!
The combi would obviously give us hot water whenever needed but losing the tank means my wife can't have her powerful 3 bar shower pumps and also there'll be no emersion heater if the boiler fails!
I'd also like to have the options to fit solar heating to the tank at a later date.
I've read and been told that oil boilers aren't great at being combi's as they don't like being cycled on and off all the time? I've also heard that separate pumps could be added so we can have the high pressure showers with a combi? I would like a system I can repair easily myself if something goes wrong (not the burner parts of the boiler though)
I'm confused!!!
Any advice is appreciated.

 

[Burdekin]

I like combis and we have an oil combi at the cottage and works a treat. We have good mains pressure and I like a big locker room style overhead shower and a very hot shower and the combi handles it no bother but you need to spec it correctly.

 

[dobbslc]

Thanks!
If I cock it up and the shower pressure drops she'll cut my @@## off!

 

[Burdekin]

Thanks!
If I cock it up and the shower pressure drops she'll cut my @@## off!

A decent hot shower is a life necessity so I know where she is coming from...

 

[Kayos]

I’d go system boiler with either a thermal store or unvented cylinder

Best hot water going and either will allow solar panels in the future (if you buy wisely) but ultimately site conditions would be the deciding factor

Modern oil combi’s are pretty good but a combi is not a 1 size fits all solution

 

[HughF]

I would second what kayos said - unvented or thermal store with a spare coil for future solar.

 

[dobbslc]

Thanks, what's the difference between a thermal store and an invented cylinder?

 

[maz0]

Good choice with replacing the whole system. I bought a house several years ago which was all micro bore and older radiators (which we cleaned with a pressure washer inside), we replaced the boiler with a brand new combi and had nothing but trouble for 5 years....we had a 5 year warranty with the boiler and there was an engineer out replacing parts every 4 months. In the end it was finally figured out to be the micro bore pipes were full of gunk and crap that was blocking the heat exchanger, and you cant exactly start re-piping the place when you have a few grand of hardwood flooring down by then.

 

[Dcal]

First thing you need to check is what is your mains pressure and flow?

If you have dodgy mains and are at the end of long length of 1/2" plastic pipe your options will be reduced.
If you don't have a cold water tank both the hot and cold water will be coming through the mains and the reduced flow might cause "friction" between you and your better half.

I do have good mains and did something similar recently.
I went for a condensing oil boiler and an unvented hot water tank with a couple of extra coils for upgrading to solar heating (when I get the time)

I kept the central heating vented as it was less bother as I wasn't changing anything on the radiator side.
Everything shutting down when you lose pressure and you are away for work is also a pain, unless your wife knows how to use a filling loop!

 

[wookie]

Forget the combi, it's a failed idea as far as I'm concerned.

At our last house in the summer when the water board turn down the pressure to stop people wasting water with a hosepipe our combi used to stop working due to low pressure, every year we had to ring them up and complain to get the pressure turned back up a bit, even then if a couple of the neighbours were using their hosepipes the combi wouldn't work. Get in from work and want a shower, nah, had to wait until 9 or 10pm when everyone had finished watering their lawns.

If your water is off you can still wash your hands with the hot you have in the tank, our water has been off 4 times this week due to mains pump failures & burst pipes.

A well lagged cylinder doesn't loose that much heat, I've also lagged the hot pipes through the entire house. Also with a cylinder you can add solar, given the amount of sun we've had this year I'm regretting not installing solar hot water.

 

[HughF]

Thanks, what's the difference between a thermal store and an invented cylinder?

Google will answer this better than I can be bothered to type out on my phone...

 

[julianf]

Thanks, what's the difference between a thermal store and an invented cylinder?

Unvented is a tank of water, under pressure. The contents are what comes out of the tap.
Must be installed by someone with the right papers.

Thermal store is a tank of dirty water, which never changes. Your dhw is heated on demand, usually by a finned coil inside the tank, but sometimes with flat plate exchangers and pumps. It can be installed by anyone subject to the usual BC stuff.

We have a thermal store downstairs, on a concrete floor. It's fed directly from our Rayburn (ie same water in Rayburn's back boiler as in store) but also has high recovery coils for a non-combi boiler and solar thermal.

Pressure to the dhw coil is limited to 3bar with a regulator, and there is a small expansion tank post coil. This gives us mains (ish) pressure hot water upstairs, and all the taps in the house are potable water. We fill the kettle from the hot tap.

The disadvantage of a thermal store is that you can not use all of their volume, as the tank temp drops from use. Whilst a mains pressure tank allows you to use the entire volume. But thermal stores are much easier to work with with solid fule etc. as there all vented from the offset.

 

[HughF]

Thermal store also known as a buffer tank. My Dutch friends have 1800l of buffer capacity heated by a 50kW peat/coal/pallet burner, they also have a couple of spare coils and plan to add solar. The dhw coil has a large surface area and is capable of supplying all required hot water on demand. They are a great system.

 

[Kayos]

You can’t connect an uncontrolled heat source to unvented but can with a thermal store

As a few have said, it’s all down to site conditions, low flow isn’t always an issue as there are various booster pumps and accumulators available

 

[Kent]

If it's a combi only buy the bosh, you have been warned.

I run a combi and run of natural spring but I do have a guaranteed pressure from a 1500 litre tank in the pump house where is gets uv particle filter and pressurised.

Only the bosh not the warm flow whatever remember.

 

[HughF]

If it's a combi only buy the bosh, you have been warned.

I run a combi and run of natural spring but I do have a guaranteed pressure from a 1500 litre tank in the pump house where is gets uv particle filter and pressurised.

Only the bosh not the warm flow whatever remember.

Interesting, we are also on private water supply. Not many of us about

 

[Kayos]

Interesting, we are also on private water supply. Not many of us about

I was involved in updating a heath Robinson pump house feeding 6 properties in North Yorkshire

One owner refused to pay so he was just connected up as we had no choice really, once it was done he wanted access to the pump house to alter the pipe crossing his land and none of the other residents would give it to him

 

[HughF]

We have the spring in our own field , no-one else has access to it or uses it. We are very isolated.

 

[Kayos]

This had a system that had “evolved” over the years

Devolved would be a better word actually

 

[HughF]

I can imagine having a private supply feeding many properties would be an issue.