System boilers vs combis for areas with hard water

[stewamax]

I have just been looking at whether it would be better for my daughter (who lives near Bath and has the area's notoriously hard water) to change her combi boiler for a system boiler*, i.e. one with an external indirect DHW cylinder. Any scaling up would then be on the cylinder's heating coils (and on the inner surface of the cylinder - which might improve its insulating properties!) and since this should be a slow process over a large surface area rather than the relatively tiny working surfaces of a plate heat exchanger or diverter valve, such a system should be much more proof against the 'death by hard water' so prevalent in boilers in the Bath area.

i would be interested to know if there is a deliberate preference for system boilers (or even regular vented systems) over combis in areas of very hard water.
My daughter could of course fits a salt-based water softener in place of her current Combimate; the latter do work up to a point, but Bath water is mighty strong stuff

* I would for preference pick a boiler with an external motorised valve for DHW rather than an internal diverter; a doddle to fix when the synchron motor needs changing and pretty simple even when the valve itself gets corroded

[Devjon]

Hi Stewamax,

We too live in a very hard water area. We have a traditional "Y Plan" heating system with a cold water tank and CH expansion tank in the roof. This runs off a Glowworm "Ultimate" boiler with an external 3 port valve. ( the syncro motor failed a few years back and it was a 5 minute job to change it myself )

The system has been in place for about 22 years. The Hot Water tank sprung a pinhole leak last year and we had it replaced by a local Plumber who was recommended by the people who service our boiler. When he took the old HW tank out I was curious as to how much limescale had built up in the tank.

The plumber cut the top off and we were both surprised by the lack of limescale. There was a very fine milky residue on the bottom of the tank but apart from that, no evidence of limescale build up at all.

A couple of points which may or may not be relevant, I never used the Immersion heater element in the tank to heat the water, it was always heated indirectly by the coil. A work colleague who used the immersion heater exclusively to heat the hot water tank had a significant amount of scale inside when his tank failed after a much shorter lifetime than ours. Perhaps the greater surface area of the heating coil is "gentler" on the water than in the immediate vicinity of a 3KW element.

I also have had one of those Electronic "water softener" gizmos where you wrap a couple of aerial wires around the pipework and it is supposed to help prevent limescale buildup. Now, I'm not convinced by the ( lack of ) science behind it, but I got it for next to nothing through work and it only costs pennies a year to run.

One final point. The woman who services our heating was apprenticed to the man who used to service our boiler before he retired. She is excellent at her job and very knowledgeable. When our boiler started to play up a couple of years ago she diagnosed a faulty boiler thermostat which she fitted the next day. I said that as the boiler was over 20 years old perhaps it was time to change it. She advised against it saying that these types of boilers are extremely reliable, tend to go on forever and be more trouble free than a "Combi"

[jackdaww]

ive had a standard boiler with seperate hot water cylinder and expansion tank for nearly 20 years now.

very little trouble from a simple system if you have room for the tanks .

ive heard of many problems with the more complicated combis and condensing boilers.

[bruncher]

I have rented four houses in the last 10 years, three with combis (newish) and all had to be adjusted for loss of pressure, and two had permanent leaks which seemed to be accepted as normal for the type of system.

[Pheidippides]

I live in NW Kent, so super-hard water here as well.

I am a firm believer in water softeners. It was an early purchase when I bought my first house in 1987 at the recommendation of my late FIL. As far as washing machines and showers go it is certainly worth its weight in gold (or salt). I've had three different models over the years and, in my view, the Kinetico 2020 is peerless

I recently (3 years ago) switched from an indirect system to a combi in the loft. It saved me a ton of wall-space in the kitchen, freed up the airing cupboard and gave me more space in the loft when all the old tanks were removed.

I would not even have countenanced this change without a water softener. So far (touch wood) the combi has behaved fine, topping up the pressure is easy - our biggest problem has been the batteries in the wireless thermostat.

Regards

Pheid