can I use 2 Magnetic filters on boiler

6 Oct 2015
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United Kingdom
hi all,

Recently bought a new house, and I have come to learn that the boiler has a magnetic filter fitted to the Flow pipe.

After some digging on this site, the general consensus is this should be fitted to the return.

There is ample room to fit this on this return.

So I have 2 options.

1. Leave existing filter where it is and add a 2nd filter to the Return. (My preferred option)
2. Take the filter off the flow pipe and install new filter on return only. With the additional nuisance of having to put a straight coupler and new pipe to fill the gap on the flow which will not look clever.

What would those in the know suggest. Thanks in advance.
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Or 3. Don't change anything.

Have you looked in the filter? If the system is reasonably clean, I would just leave it as it is. Only if there is a lot of crud in thr filters would I consider changing anything.

Why is the return pipe preferred? I guess the aim is to catch the crud from the radiators before it gets into the heat exchanger and pump. But does it do any harm for it to pass through them just once? If you have two filters, does this impede the flow significantly?
Most instructions for magnetic filters do say the return is the "preferred" option but not strictly necessary. If there was room it does make you wonder why it wasn't put there in the first place, but I certainly wouldn't worry about it.
Start by giving the filter a good clean. Then again in a month. If there is no more than a smear of black dirt the second time, then there is not much dirt circulating. If you want reassurance, you can add a mild cleaning chemical to loosen any existing sediment. In my (DIY) experience, the filters trap a lot of dirt when first fitted, then, as time goes by, there is not much left. So you might empty it weekly at first, then monthly, and eventually it only needs cleaning once a year. If you disturb the system by working on it, or doing a drain and refill, or add a cleaning chemical, it will disturb residual dirt and the filter will then trap it as it circulates.

An old system, especially if it used to be open vented, may have quite a lot of dirt in it unless it has already been cleaned.
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OP there would be no problem with having two filters they wont impede the flow in your system, thing you need to remember is that Magnetic filters are exactly that , they will catch Magnetite that is in your system water, they wont filter anything else, there are lots of nasty particles in old systems that havent been flushed properly, but you are doing nothing wrong with using a magnetic filter, or two for that matter
So if you had 10 filters, they wouldn't impede the flow either?
If an established filter then all the dirt collection should have already occurred.

Draining and fiddling with the pipework will bring in new oxygen and probably do more harm than good.

A mag filter does all its going to do in the first few months if the system is not being disturbed.

So if you had 10 filters, they wouldn't impede the flow either?
Well smart arse back that up with some proper figures , what is the restriction on the flow of the filter that the op intends to install considering you havent a clue which one he intends to use, would it have any more restriction than adding another radiator ? you have no clue what system he has , and would adding another filter have any consequence on his system you tell me einstein
sorry OP just hate when an experienced engineer has taken their time to give you honest and proper advice and some gob shoite thinks they are a hero to give contravening advice that has no substance

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