New oil combi boiler

[Roger Hayter]

Tried archives and the general boiler recommendations seem to include Worcester Bosch, Vaillant and Viessmann. Though it is unclear if Viessmann still make domestic sizes. I probably want about 25 to 35kW.

25 would cover the CH, and perhaps it is a bit wasteful burning excess oil for hot water.

Anyone got any other recommendations, or preferences for one or more of above? Not primarily motivated by price. A boiler core which is not to easy to block or corrode would be good, but I am resigned to condensing.

Many thanks,

[tabbypurr]

Look at the Which report, 'The best & worst boiler brands' 2016. WB & V are the 2 most reliable makes. WB 92% Vaillant 83% Veissmann 76%

NT

[S Viemeister]

We have an externally installed Grant, and have been pleased with it.

[alan_m]

What was the sample size and was it self selecting participation in the survey?

As the TV adverts say, 75% of dentists (who got the free equipment and samples) agree.

[Roger Hayter]

They only seem to have information on two makes of oil boiler, and I have had enough trouble with the oil burner on mine to think it is significantly different from gas. Though the dominance of Worcester Bosch makes me wonder if this may not be best for spares anyway.

[Roger Hayter]

Thanks. That's one useful data point. Which don't seem to have been impressed, I note, but I am not sure how much I would rely on Which.

[Martin Brown]

+1 for WB. Mine has just given out and was of 1970's manufacture. I am interested in the most reliable condensing boiler options since neighbours do seem to have trouble with theirs and it is invariably due to icing up blocking of the condensate pipe or random control electronics failure (which these days means new entire controller board every time rather than just swapping out a defective relay or sensor).

What sort of problems with the burner? Mine has always behaved itself.

Any problems I had have been down to dirty fuel or sooting up of the flame sensor during extreme storm conditions. Provided you get the oil pressure right and change the filter as needed I found it very reliable.

Eventually the boiler exhaust flange rusted away aided by bat dung falling on it. My oil boiler is conveniently located in the loft :(

[John Rumm]

With a combi, you need to be driven by your hot water demand rather than heating. So a 24kW model will deliver say around 10 lpm of hot water.

35kW will get you half as much again, which can make a big difference in things like bath fill times, and also let you run two "normal" showers at once. On the downside oil boilers also tend to have a lower range of modulation than their gas counterparts - so more power may mean you are not getting as much fuel saving when running on lighter loads since the boiler will be less able to load match and hence will cycle more.

Alas those last two are kind of exclusive. Typically the small water pathways are part and parcel of getting the heat exchanger transfer rate required to let the boiler condense. This makes thorough cleaning and flushing of the primary side of paramount importance prior to fitting the new boiler. Magnetic / cyclonic filters are also worthwhile as well.

[Martin Brown]

Any recommendations for non-combi condensing oil boiler suitable for use with a thermal store and existing solid fuel back boiler?

The existing system was passive convection hot water heating from any of back boiler, oil boiler or immersion heater. In an ideal world I'd like to keep that flexibility and maybe add solar hot water to it as well.

I understand any new installation will have to be zoned and pumped.

Does that mean that in an existing elderly installation the entire central heating system will need to be swapped at the same time?

[The Natural Philosopher]

don't bother with a thermal store. use a mains pressure tank which amounts to the same. That will have immersion anyway.

And fit water softening if prone to scale., A MPHWT is expensive but dies from scale just the same.

And keep your existing boiler. What you will need are some complex valves to regulate flows through he various heating elements.

Unless you connect em all in series so your back boiler gets hot when hot water is needed.

Frankly I would think - and it's a tentative rough think - that using a existing system boiler with presumably its pump to drive primary water around the boiler, the solar heating and the back burner would be fine.

All you then need are manual or thermostatically operated valves to divert the primary heating water around such things as cold back boilers or frozen solar heating.

[tabbypurr]

You don't have to but can expect to need to solve some issues if you don't. The main reason to replace rads is that larger rads enable a CH system to work in condensing mode a lot of the time.

NT

[The Natural Philosopher]

Is that either true, or relevant to oil boilers?

Surely even a condensing boliler can manage 60C which is the upper limit for most rads?

[John Rumm]

Sounds like you would also need an open vented boiler in that circumstance, unless you opt for a separate heating coil in your cylinder / store for the solid fuel heating. I have no direct experience of oil boilers, so can't recommend one.

What does your thermal store run; just DHW, or heating as well?

One option is a tall cylinder with more than one heating coil - the solar at the bottom where it can dump its "low grade" heat into the cooler water.

Not necessarily. Condensing systems tend to perform better with lower flow temperatures, and so in some circumstances larger rads may help. Having said that in many cases it will work fine with the existing ones unless they were only marginally adequate in output power in the first place.

[tabbypurr]

n't. The main reason to replace rads is that larger rads enable a CH system to work in condensing mode a lot of the time.

Larger rads do enable a condensing boiler to run condensing more of the tim e

relevant to any condensing boiler

yes, though I'm unclear how that would be relevant to the question

If there's an upper limit of 60C in rads it's news to me. And again nothing to do with the question. Small rads that require high flow temp inhibit condensing when high output is required, the flow temp becomes too high to condense. Larger rads keep f low temp down, improving fuel efficiency via lower flow temp and thus conde nsing operation more of the time.

NT

[Roger Hayter]

Riello burner. Oil pump seals twice (life < 5 years), light dependent resistor out of spec (twice), electrolytic capacitor in the spark transformer driver. Apart from what should perhaps have been preventative maintenance, flexible pipe leaked, jet worn, sooted up spark gap. No problems with pressure, air flow on the safe side, if not most efficient.

[The Natural Philosopher]

radiators are operated at around 60C peak input temp. Any more than that and you burn the toddlers

In fact lower temps are more normal

Only thing that needs to be 60C is DHW tank

Any Condensing boiler fan ee3sach around 60C without losing any condensation

[John Rumm]

Its the return temperature that matters more since this dictates how cool you can get the flue gasses.

You can still have a high flow temp if you want, but may need to run a bigger DeltaT across the rads. (condensing systems are often balanced to drop 20 degrees across a rad rather than 11)

Oil boilers seem to get less condensing efficiency gain than gas ones in the first place, and are also often hampered by having a smaller range of power modulation, which makes them less able to match the actual load year round.

[tabbypurr]

don't. The main reason to replace rads is that larger rads enable a CH syst em to work in condensing mode a lot of the time.

hing to do with the question.

put is required, the flow temp becomes too high to condense. Larger rads ke ep flow temp down, improving fuel efficiency via lower flow temp and thus c ondensing operation more of the time.

Mine doesn't seem to consistently condense at 60C flow temp, fwiw. Flow temp really depends on the rads, and rads vary depending on when they were installed. Old rad setups were typically designed to produce lower ind oor temps than are general today from quite hot water.

But shrug... it just depends what you've got.

NT

[Roger Hayter]

As a follow up for all those who gave advice; my preferred plumber (who can also do the job in 2 weeks) only does WB, and I am happy with that (32kW model), though not overjoyed at the cost.

(Urgency being as my Firebird Olympic Combi has rusted through the steel heat store at 14 years old, and they haven't done spares for 7 years. Would I buy another one? Not that I bought this one.)

[Michael Chare]

I have two different non condensing Worcester Bosch boilers, but I have been rather put of the company when they refused to answer technical questions when I truthfully said I was a householder rather than an engineer. They did provide some information, but they could have told me exactly what the fault might be which they did not do.

One consideration is the burner. Riello were quite helpful when I spoke to them some time ago, and all the parts then come form Riello, apart from the jet itself.

Grant is another manufacturer to add to your list.

You can learn quite a bit about boilers by downloading the installation instructions.