Pump for boiler descaling

[Martin Pentreath]

Hi all,

I have a intergas boiler with a developing limescale problem on the domesti c hot water side. Taking the heat exchanger out looks to be impractical, so I thought I'd try the alternative technique of circulating descaler throug h it in situ by connecting up a pump and a bucket of DS3 descaler to the ne arby hot and cold washing-machine valves.

I can easily pump cold water through the heat exchanger this way, but as so on as I introduced hot water (by pouring it into the bucket) the pump gave up. To be fair it was the cheapest drill-attached pump I could find:

Any suggestions for a pump which is up to pumping hot acidic water?

Cheers!

Martin

[John Rumm]

Have you got a spare CH circulator pump?

Failing that, could you use two buckets and a bit of gravity - place one with the DS3 higher, and let it syphon through to the lower one?

(you would have to manually empty the lower bucket back into the top again from time to time!)

[Harry Bloomfield]

Martin Pentreath explained on 16/02/2018 :

A normal electric central heating pump should be OK for that, but they are not self priming, so would need to be sucking from a water level above them. Bucket above the pumps level.

[Martin Pentreath]

Thanks John and Harry. I was just looking at cheap central heating pumps, although the siphon idea appeals to my tight fist. I might give it a go first.

[tabbypurr]

tic hot water side. Taking the heat exchanger out looks to be impractical, so I thought I'd try the alternative technique of circulating descaler thro ugh it in situ by connecting up a pump and a bucket of DS3 descaler to the nearby hot and cold washing-machine valves.

soon as I introduced hot water (by pouring it into the bucket) the pump gav e up. To be fair it was the cheapest drill-attached pump I could find:

do you need to circulate it? Fill & let sit should work

NT

[Brian Gaff]

Something like an eversible bilge pump? Brian

[newshound]

Certainly what I would start with, on the KISS principle.

That said, small 12 volt bilge pumps are pretty cheap, I have one knocking around somewhere that I used for another little project. No electrocution risk!

[James Wilkinson Sword]

Those things have a habit of saying "I can't be bothered getting going". They need a good head of water and no particles to clog them up (despite them claiming they can cope with particles up to a certain size). They spin ok, but just don't push the water.

[Martin Pentreath]

For the benefit of the archive I thought I should follow up with how I got on with descaling the DHW component of the heat exchanger of my intergas bo iler.

In the end I bought a very cheap submersible pump from Amazon for £27, one of these

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I put it in a bucket with about a gallon of dissolved Fernox DS3 descaler. I used one of these to connect a length of garden hose pipe to the outlet o f the pump

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I connected the other end of the hose pipe to the cold valve that feeds the washing machine. This formed the flow to pump the descaling fluid into the boiler's heat exchanger. For the return I connected another length of hose pipe to the hot washing machine valve (a remnant of an earlier era of wash ing machines), with its other end going into the bucket.

I turned off the mains water coming into the house, so what I ended up with was a circuit from the bucket via the pump through the plumbing for the wa shing machine valve, through the heat exchanger and back to the bucket agai n.

I ran the pump like this for about 20 minutes. I found that if the boiler w as switched on then the rate of flow produced by the pump was enough to tri gger the combi's flow detector and the boiler flicked on to heat the DS3 so lution as it passed through the heat exchanger, which I assumed would help with the descaling reaction. I didn't want the fluid to get anything beyond tepid for the sake of the pump so I turned the boiler off again after only about 10 or 15 seconds of this.

Everything ticked along smoothly with the fluid slowly looking a little dir ty. After 20 minutes I reversed the rate of flow by reversing the hoses in order to pump the fluid in the opposite direction in the hope that this wou ld make a more thorough job of the descaling. Then for the last 20 minutes I went back to the original direction of flow.

Finally I disconnected everything, shut the washing machine valves, turned back on the water and made sure to run plenty of both hot and cold water fr om every tap in the house to remove any traces of the DS3.

Its not as satisfying a job as removing the heat exchanger because you can' t actually see the extent to which the descaling has visibly improved matte rs. However removing the heat exchanger is not an option with the intergas boiler.

In retrospect I am not sure whether DS3 is strictly suitable for use with p otable water. However I made sure to give the system an extremely thorough flushing out afterwards. An alternative plan would be to buy substantial qu antities of vinegar, or to use citric acid, although to what extent they ar e compatible with aluminium I don't know.

[John Rumm]

Did it fix the original problem though?

If flushed out it should be fine.

[Martin Pentreath]

Here's an American video showing essentially the approach which I took, exc ept he uses a much more expensive submersible pump and also uses vinegar in stead of DS 3 as the descaling chemical.

Also Americans seem to have lovely service valves just below their boilers. These allow easy draining of the DHW heat exchanger and also easy pumping through of the descaling chemicals. See the video at 1:12. Can anyone point me in the direction of a similar type of valve to put on the domestic hot water pipes to my boiler? I reckon it would be worth a little bit of replum bing in order not to have to use the valves for the washing machine which a re not exactly conveniently located.