Cleaner poured into ch tank discolours hot water!


Postby annemarie » Tue Oct 02, 2007 11:23 am

We have a Baxi back boiler about 7 years old connected to an old (20-30 years) c/h system. The radiators were cold although the recently-serviced boiler and the pump were working ok. We called a heating engineer who said there was a blockage and we needed to put a cleaning solution into the little cistern-like tank in the airing cupboard by the hot water tank. He did something which got the radiators hot, however they cooled down again shortly after he left.
We put the cleaner in the tank one evening, by the next morning the hot water supply was discoloured a deep green!
We poured away the hot water and let it refill several times and it is clear now.
In addition, two of the six radiators (both upstairs) are permanently hot even if the c/h is off. This is a new problem since the engineer visited. I complained to the company who said the room thermostat is at fault, but two other radiators are obeying the room thermostat (the other two, both downstairs, are permanently cold) so I don't think this is correct.
They would not tell me what the engineer did so I don't know if he caused the problem with the cleaner getting into the hot water system. They said he did nothing, but he told me that he had done something to do with some valves under the tank that control the relative amounts of hot water getting into the ch and hot water systems.
We need to be able to get the cleaner into the system as I think a blockage is the main problem, but I think most of the cleaner got into the hot water supply and I don't want to add another bottle till this is sorted out. Can anyone tell me how it may have happened? The most obvious question is, did we put the cleaner in the correct tank?
Thanks in advance for your help.
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Postby htg engineer » Tue Oct 02, 2007 8:11 pm

[quote]The most obvious question is, did we put the cleaner in the correct tank?[/quote]

Probably not, it sounds like the cleanser was put into the domestic hot water supply.

The room thermostat doesn't control individual radiators, it controls the pump, when the temperature of the room falls or increases it will form an electric circuit which turns the pump on or off. The only cost effective way of controlling individual radiators, is to fit TRV's (thermostatic radiator valves).

Upstairs radiators will get warm on a gravity hot water system, this is because heat rises. If radiators are getting hot, altering the boiler pipework so that there's a 'trap' like bend on the heating flow where it leaves the boiler will prevent the upstairs radiators getting hot.

There are a few ways of getting cleanser/descaler into the heating system. Firstly is the way you tried, adding it via the tank. But you can also inject it using a special bottle into a radiator vent. Or remove a radiator, fill with cleanser then replace.

Hope this helps
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Postby The Heating Doctor » Tue Oct 02, 2007 9:32 pm

Are you sure you poured the cleaner in to the small 4 gallon feed & expansion tank? Sounds from what you are saying that the cleaner was poured in to the cold water storage tank feeding the hot water cylinder this is the only way the cleaner could have enterd the hot water system.

To help identify each tank the
approx size of each tank would be as follows

feed & expansion tank Size: 442(l) x 296(w) x 305(h)
cold water storage tank Size: 736(l) x 584(w) x 533(h)

Each tank should have a 60mm thick insulation jacket around it.
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Postby annemarie » Wed Oct 03, 2007 10:16 am

Thank you both for your replies. It does look like it was the wrong tank. The tank I used is 42cm x 24cm x 14cm, is attached to the hot water tank at the top, looks like a small toilet cistern without a lid and has two pipes going into the hot water tank. I'm horrified because the central heating engineer told me to use that tank. According to my reference book, the feeder / expansion tank is in the loft, so I put my hand into the tank he indicated and asked if he meant that one, and he said yes. I won't be using that company again!
At least the cleaner is not carcinogenic - I phoned the manufacturer and checked.
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