Combi Cycling w/mixer shower

So I fitted a mixer shower to replace the electric shower that attempted to set fire to our bathroom a month or so ago[1].

Heeding warnings about water flow rates etc due to much trawling of Google Groups and reading of FAQs I have ensured that as much of the hot run from the boiler to the shower is 22mm as can be and there are as many wide sweeping bends (as opposed to corners) as I can get away with.

The shower head also has nice wide holes and the pipe is fairly wide diameter. The shower is like standing under Niagra Falls compared to the old one and the water projects nicely from the head.

The problem is that the boiler cycles on/off - it is a modulating boiler, BTW. This doesn't seem to affect the shower much, the flow rate and temperature do fluctute a bit, but it isn't uncomfortable.

Now, I know the feed to the boiler is poor (15mm, for a start) and was assuming I would have to get this replaced anyway - my neighbour (a general builder) reckons I should get it tapped directly into house supply from the main, if possible. I shall consult a plumber, as this sounds like serious getting wet work...

Anyway, having the subject of limescale in/around the DHW heat exchanger is mentioned in a couple of articles. I'm worried about this as we live in a very hard water area. I'm wondering if there is anything I can do to ascertain A) if there is a problem and B) do something about it if there is? The boiler is probably 8 years old now. We had the entire CH de-limescaled and de-sludged a while ago and it made a hell of a difference, could this be a problem for DHW?

I'm going to get the boiler supply replaced anyway, just want to know if there is anything else that could be affecting it.

Well that was about 80 lines more that I'd hoped I'd have to write.

Thanks, any help would be greatly appreciated.

Reply to
Andrew Collins
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It is unlikely to be related to the size of your pipework. Provided you don't have low pressure or flow rates from your supply, 15mm isn't likely to affect a combi hot water system. Indeed, 15mm would have the advantage of less dead time waiting for the hot to come through.

I would certainly suspect scaling up of the heat exchanger on the DHW side. If the hot water side hasn't been descaled in 8 years, there is a good chance that it has a nice coating of limescale. The primary side should be OK. This side doesn't get fresh water, so all the hardness will be long gone, provided you aren't constantly topping it up.

Christian.

Reply to
Christian McArdle

I have one that works.

Reply to
IMM

You could have the heat exchanger descaled, but generally it's more sensible to replace it.

There are two solutions to preventing scaling from hard water.

1) A phosphor dosing unit such as a Combimate installed before the boiler. This uses a chemical dosing agent which is very slowly released and needs replenishing about once a year. The unit costs approx £100 and refills about £20. This technique basically prevents the deposition of the calcium and magnesium salts on the surfaces of the heat exchanger. It does not soften the water or provide any reduction in the use of detergents and shampoo.

2) An ion exchange water softener. These genuinely soften the water by exchanging the calcium and magnesium ions in the water for sodium. This is achieved by passing the water through a column of resin beads which are then periodically regenerated using a brine solution. Softeners do this by use of a timer and regenerate during the night or by a metering device which operates based on water use and typically results in less salt use. Ion exchange softened water reduces detergent and shampoo use by 30-50% as well as preventing any deposition of scale. Over a period of time softened water will also redissolve scale in appliances, but it can take a matter of months. Water softeners cost in the range of £300 to £1000 depending on type, capacity and control sophistication. To give you an idea of running costs, in a house of 4 with a lot of water used, I get through a 25kg bag of salt (cost about £5) every 3 weeks. However this is more than offset by the saving in detergent and shampoo costs before the reduction in appliance descaling or part replacement cost is considered.

Two other points.

- Don't bother with electromagnetic/magnetic water treatment devices. They are not effective in this type of application.

- If you needed to desludge your heating, it won't have had a scaling problem because the water is fixed in circulation. The main issue is sludge due to corrosion. Hopefully you added some inhibitor.........??

.andy

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Reply to
Andy Hall

We know...

Reply to
Grunff

I said "in this application".

If you thought that it would be any more effective than chocolate hot water plumbing (to extend a metaphor), it is notable that you didn't propose it.

.andy

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Reply to
Andy Hall

Ouch. Looks like I may have to warm up a credit card...

I'll probably go for one of these.

But IMM has one that works :) - yes I've read a few of those discussions.

Yup. I mentioned limescale as the rest of the heating system is of untold age. There was a back-boiler that was replaced with the new combi one some time in the mid 90s. I suspect, from the design of the fire that I recently skipped along with the boiler that had never been removed, that it was 70s, possibly even 60s. The CH system also leaked like a sieve until I fixed it last year (when it was de-sludged).

Thanks,

Reply to
Andrew Collins

I now propose it.

Reply to
IMM

That's OK then. God is in his Heaven and all is right with the world.

.andy

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Reply to
Andy Hall

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