DIY Doctor

Combi boiler pressure and topping up

Postby Buffy39 » Sat Jun 19, 2010 7:59 pm

Hi everyone,

I am new to the forum and a total incompetent! I would like to improve, however.

Anyway, I currently have a question relating to my Worcester Bosch boiler (a condenser, I believe). It is about three years old at the most.

In March, I topped up the pressure and then got it serviced by the people who put it in.

Now, about two and a half months down the line, I think that the pressure may have dropped by 3 to 4/10 of a bar (less than the half bar bit).

I have checked all the radiators thoroughly around the valves and the outlet pipe for leaks and nothing much seems amiss. There is some vedigris around the outlet pipe but I am fairly certain that this may be due to multiple urination by multiple cats. I am currently removing this with tomato ketchup (the verdigris, that is).

My question is whether I should be worrying about this little drop. I do tend to get rather airy radiators but have not bled them of late. Otherwise, I would have known to top up the boiler.

I look forward to having the benefit of your collective expertise.

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Simply Build It

Postby plumbbob » Sun Jun 20, 2010 4:08 pm

The pressure in a system will fluctuate slightly as a matter of course. Now it is June and the heating is off and fully cooled down, you might expect to see a small fall in the pressure anyway.

If you do have a leak, it is very small, and you are not going to see a puddle or anything like that. This type of weep will show as a build up of greenish salts around the area. There may be no evidence of dampness even as the water is evaporating naturally.

Don't pressurise it now. Wait and see if it falls further over the next few weeks. If you only need to top up a couple of times a year you should not be too worried.

Incidentally, closed systems should not suffer from circulating air. It can't get in. Maybe this might be an explanation of your dropping pressure. The air was trapped when the system was filled and it has slowly been released by the auto bleed valve causing the fall in pressure.
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Postby Buffy39 » Sun Jun 20, 2010 9:18 pm

Oh, thank you so much.

This would explain a great deal. The trouble is that I know so little about such things: I did not even know that, as a householder, one had to top up the system - I had not touched it for well over a year at one point and had bled the radiators in the meantime, and then wondered why the pressure was low.

It was thus that I took instruction from a truly lovely male colleague of mine in matters concerning keys and filling loops with a successful result.

I do have a few bits of green around the odd radiator valve but I suspect that this is oxidisation due to cat urine rather than a sheer leak. The clue is the presence of this delectable substance on the radiator itself. Once the radiator is hot, it acts as a "diffuser".... ugh!

Frankly, I live in fear of oceans of water invading my living space and can now sleep easy in my bed knowing that this is unlikely to come from my central heating system.

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Postby eggers » Mon Jul 05, 2010 9:08 pm

have the expansion vessel checked, and check to see if any water is escaping through the pressure relief pipe
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