Which Boiler?

[gabutt95]

All,

I will be replacing my old oil boiler with an oil condensing unit.

Any advice on makes would be appreciated.

Would a condensing combi boiler be worth considering?

 

[D_Hailsham]

Would a condensing combi boiler be worth considering?

That will depend on (a) the incoming cold water flow rate and pressure, and (b) your maximum instantaneous hot water demand.

You can measure the flow rate using a bucket, which is usually marked with litres, and a watch. Do it at the kitchen sink with the cold tap full on. The pressure is harder to measure, but it can be estimated if you have a garden tap straight off the mains. Turn the garden tap on full and repeat the flow rate measurement at the kitchen sink. The smaller the difference in the flow rate, the better.

Hot water demand will depend on how many baths, showers, taps etc could be in use at the same time. Assuming the incoming flow rate is 20 litres/minute and a shower uses 10 litres/minute, the maximum you could have would be two showers. Don't forget that both the cold water and the hot water are fed from the same incoming cold water supply.

 

[gabutt95]

D_Hailsham

Thanks for the info. Is there a difference from a relabilty/maintenance/servicing point of view between a combi and a standard condensing boiler??

 

[Alfredo]

Combis are effectively a complete heating/Hot water system in a box, so there is more to go wrong, and more electronics to control them (usually)

The burner/gas valve side is no different as a rule. In a combi however there is a diverter valve to switch boiler water from CH duty to HW duty, and this is governed by some kind of flow switch that recognises when you have turned on a hot tap. These sensors can fail or jam with muck (depending on type) and diverters can stick, and repairers need to decide if this is from a signalling failure(electronics) or dirty water jamming the diverter.

Its also more important in a combi that the system water is as clean as possible otherise you risk blocking the Hot Water plate to plate heat exchanger and thus ruining hot water performance.

In spite of all this I do quite like combis as they are very easy and convenient to live with. I've just sold my old house with a ten year old combi in it that had one small fault in ten years, and I really liked it. They are brilliant for showers as well as you get mains pressure HW as well as CW

The deciding factor to my eyes is your H.W. water needs as a combi will really only feed one tap at a time effectively, so no use in a big house or a multibathroom house. You also need reliable good local water pressure to keep a combi happy. Its a considerablt bonus too if your hot water pipe runs from the combi to the hot taps is reasonably short as the delay in getting HW at the taps can be irritating to some people.

Alfredo