Recommended Leak Sealer

Calibos

10 year old system with 16 radiators and Baxi Megaflow HE28. Over the last year the system has been losing pressure over the course of a month or so and lots of air bubbles audibly going through the boiler. I'd refill by opening the refill valve and within a week or two the bubbling would be back and a week or two after that the pressure would get sub 1 bar and I'd top it back up to 1.5bar again.

A week or so after its annual boiler service the boiler stopped working with an error code and the pressure had dropped to zero bar. Got the service engineer back out and he said my bleeding the radiators was some of the pressure loss. He fixed my refill valve that had ceased shut. He couldn't see anything else wrong other than the pressure expansion vessel had deflated so he pumped that back up.

Everything seemed to work fine for another week or two but then the bubbles and pressure loss was back. I went back to refilling. The boiler developed a water leak from the emergency pressure relief valve on the top of the boiler so I called the engineer back. He gave the boiler a good going over, checked everything again, replaced a water drain pipe, both top and pump pressure relief valves and assured me that the pressure drop is definitely not being caused by the boiler and that it looks like its indeed a water leak in the pipes to the rads. It can't be anywhere in the upstairs heating zone as we'd see evidence of it in the downstairs ceilings so it must be in the downstairs zone under the concrete floors.

The boiler engineer said that a Leak Sealer should fix it. When I asked, he said its probably DIY'able. That I should shut of both valves to the Towel Rail in the bathroom, open the locking nut on one of the valves and drain a few liters out of the rad, then open a nut on the top o the towel rail and refill with the leak Sealer before reversing the process. Central heating all zones back on and that would circulate the Leak Sealer to where its needed.

So my question is which leak sealer product to you guys recommend and how many litres should I buy. Were the Boiler engineers instructions correct. How long does the C/H need to be on to circulate it. How long does it take to seal the leak.

Finally, in a 10 year old system, do I need to worry about oxidisation, rust, sludge in the system from refilling from 0 or 1 bar to 1.5bar every month or so over the last year with fresh oxegenated mains water? Should the system really be drained and flushed instead and re-inhibited and leak sealed by a pro?

Thanks in Advance.

Lenar3556

Before you go down the road of a leak sealer, it’s important to rule out an expansion problem.

The symptoms you describe could well be that of inadequate expansion capacity.

There is a procedure to recharge the vessel, and it involves isolating it from the system first, I wonder did he do that?

In the circumstances I would suggest replacing the expansion vessel first, and with one of decent capacity as many are undersized. I wouldn’t go any smaller than the below.

https://mybuildingsupplies.ie/product/expansion-vessel-standard-18l?gclid=CjwKCAjwxuuCBhATEiwAIIIz0frPjsK_oE5oGwpKy38yDPOIyAvrXs3E4zcrYeL1kSfoTrUElIV-UxoCKiMQAvD_BwE

Sludge shouldn’t be an issue with a 10yr old installation, but if you keep filling it up with fresh water I will become one. Leak sealers are hit and miss and you would only pour that stuff in as a last resort.

Calibos

The expansion vessel is the one built into the Baxi Maegaflow boiler itself. Its jerrycan shaped (Squarish) about 1ft in 2 dimensions and about 6 inches wide. He recharged it with an electric air pump.

Could sizing of the expansion vessel for the size of the CH system be an issue if this pressure drop problem only cropped up in year 10? Wouldn't it have been an issue from the get go if it was too small for the CH system?

Lenar3556

Calibos wrote: »

The expansion vessel is the one built into the Baxi Maegaflow boiler itself. Its jerrycan shaped (Squarish) about 1ft in 2 dimensions and about 6 inches wide. He recharged it with an electric air pump.

Could sizing of the expansion vessel for the size of the CH system be an issue if this pressure drop problem only cropped up in year 10? Wouldn't it have been an issue from the get go if it was too small for the CH system?

The onboard explanation vessel sometimes isn’t large enough for the connected system and an additional one needs to be fitted.

Fair point on what has changed since, but that’s assuming the onboard vessel is performing satisfactorily and that he isolated it before recharging it. Otherwise the precharge pressure will be incorrect.
I would try and head it all off by fitting and additional vessel in the hot press.

The indicators are more in keeping with an expansion issue than a hidden pipe leak - which is good if it proves to be the case, because it will be much easier resolved.

Wearb

Would turning off half-ish of the radiators reduce the volume of water required and work as a test to see if the expansion vessel is undersized.
Might need both rad valves turned off, but not sure. Don't think so.

Calibos

One thing I forgot to mention is that the condensate and I presume emergency discharge pipe are T'd into one pipe that rather than going through a wall outside goes to the soil pipe/stack/shower/toilet drain pipe or whatever its called. Thus one can't tell if the boiler is discharging water because theres always some trickle or evidence of wet pipe when one lifts the inspection cover in the back yard because of every other gutter, toilet, shower, bath and sink flowing through that sewage line.

Calibos

Another thought. Would the air thats getting in the system be evidence of one cause or the other. What I mean.....and remember I don't know WTF I am talking about....is if the expansion vessel is undersized and can't accomadate the full expansion of the hot water, its purging the excess water out the discharge pipe which then leads to a pressure drop when the water cools down. But would air be entering the system when that happens? Whereas if it was a leaking radiator pipe under the concrete ground floor slab air would get sucked into the leak hole. Like I said a few days or a week after I refill the bubbles sound going through the boiler starts again and I can even hear gurgling in my bedroom rad which is in the attic conversion at the same level as the boiler. WHat I usually do when I know the system needs a refill again is to bleed that air out of my bedroom rad which is where most of it seems to collect, and only then open the refill valve to top up the system to 1.5bar again.

K.Flyer

Given as you say that the boiler is in the attic, if the pressure drops enough it could pull air in through the boilers internal auto air vent.
You need to check the system pressure from cold to when the system is running at full temperature to determine if the expansion vessel needs closer attention (although given the typical size of a boiler vessel and that you have 16 radiators, I would think it is undersized and an additional vessel wouldn't be a bad thing).
Firstly fill the system to a minimum of 1.00 - 1.25 bar when the system is absolutely cold.
Then run the heating system until it is up to full temperature, so at least 30 minutes.
Check the pressure gauge on the boiler over the time and you should really only see approx 0.5 bar increase at most. If it starts to climb up to >2.5 bar then you have an expansion vessel problem. This could in turn cause you to loose pressure by the pressure relief valve lifting or water getting out through a weak connection.
Do the pressure check first before looking for other issues.

Calibos

K.Flyer wrote: »

Given as you say that the boiler is in the attic, if the pressure drops enough it could pull air in through the boilers internal auto air vent.
You need to check the system pressure from cold to when the system is running at full temperature to determine if the expansion vessel needs closer attention (although given the typical size of a boiler vessel and that you have 16 radiators, I would think it is undersized and an additional vessel wouldn't be a bad thing).
Firstly fill the system to a minimum of 1.00 - 1.25 bar when the system is absolutely cold.
Then run the heating system until it is up to full temperature, so at least 30 minutes.
Check the pressure gauge on the boiler over the time and you should really only see approx 0.5 bar increase at most. If it starts to climb up to >2.5 bar then you have an expansion vessel problem. This could in turn cause you to loose pressure by the pressure relief valve lifting or water getting out through a weak connection.
Do the pressure check first before looking for other issues.

Just getting back to this thread now.

Pretty sure the system was warm/hot when the engineer isolated the system to replace the valves and overflow flexi-tube and after he left with the system running and topped up it was 1.5bar with the pressure gauge in line with the adjustable pressure marker dial at the 1.5bar marker. When the system is cool it drops back to about 1bar and then when the heating zones comes back on the next morning it rises back to the 1.5bar marker, so it is indeed looking like only a 0.5bar rise on the pressure gauge when the system is hot.

Tis about a fortnight since the boiler work and the pressure hot/cold hasn't dropped much from the 1.5/1.0bar level so it doesn’t look like it's lost much pressure yet in those 2 weeks but the bubbles noisily going through the boiler is back already.

Though I suppose that could have been the air already in the system when the boiler work was done. Perhaps I need to bleed all the rads again to purge it one last time, then top back up to 1.0bar cold or 1.5bar while hot. If the pressure holds for a couple of weeks with no new bubbles noise, then that would indicate no leak and it was indeed a boiler issue all along wouldn’t it?