Author Topic: CH Boiler running at too high pressure  (Read 2846 times)

CH Boiler running at too high pressure
« on: 29 October, 2017, 09:45:44 am »
As above, when I run the heating (as opposed to the HW) the needle goes well into the red.
Instructions on the lid tell me to release water from any radiator until the needle drops back into the black.
I've found a rad which has a drain tap fitted.
Do I do this when the heating is running or with it off?
*Knows Very Little About How CH Works*

Re: CH Boiler running at too high pressure
« Reply #1 on: 29 October, 2017, 09:53:27 am »
That is often a symptom of air in the system.

You don't need to use a rad with a drain tap to bleed off some water, just use the rad air bleed valves.

But I would run your heating until rads are hot, go round all rads and check for any with cold spots. Bleed these off to try to eliminate any air. Do this first.
<i>Marmite slave</i>

Re: CH Boiler running at too high pressure
« Reply #2 on: 29 October, 2017, 10:50:09 am »
This can be due to lack of air in the expansion vessel.

If that is the case, let the system cool down and then release the water pressure from the system. Then fill the expansion vessel with air up to around half the normal working pressure of the system. There is a schrader valve in the top of the expansion vessel for that. The water pressure should stay/be kept at zero while that is happening. Use a type pressure gauge for the air pressure. When that's done, re-pressurise the water system to the normal pressure.

The expansion vessel has a diaphragm to keep the air from the water, and to hold some air as a buffer for when the water expands as it heats up. If there isn't enough air, the pressure rises more than expected as the water expands.
Quote from: Kim
Paging Diver300.  Diver300 to the GSM Trimphone, please...

Aunt Maud

  • Le Flâneur.
Re: CH Boiler running at too high pressure
« Reply #3 on: 29 October, 2017, 01:37:24 pm »
Not enough air/too much air, blimey.

Re: CH Boiler running at too high pressure
« Reply #4 on: 29 October, 2017, 02:03:11 pm »
Bleeding the rads appears to have done the trick.
Thank you Mr. C  :thumbsup:

Phew! Waaaay to mild to be running the CH today.

Re: CH Boiler running at too high pressure
« Reply #5 on: 29 October, 2017, 04:29:27 pm »
No it hasn't fixed it  :(

Re: CH Boiler running at too high pressure
« Reply #6 on: 29 October, 2017, 04:34:17 pm »
Pressure vessel is the likely cause though our boiler has a third problem.  It constantly keeps topping itself up at a trickle as the fill loop doesn't close off properly.  It was a known problem with Vaillant boilers of our vintage.   We know that this is the problem as it slowly but surely increases in pressure over a four to six week period even when the heating is not in operation.   It can be relieved by simply draining at one of the rads but the issue keeps returning.

I monitor and manage the issue as the boiler is otherwise fine.     

Re: CH Boiler running at too high pressure
« Reply #7 on: 29 October, 2017, 04:39:58 pm »
It constantly keeps topping itself up at a trickle as the fill loop doesn't close off properly.  It was a known problem with Vaillant boilers of our vintage.   We know that this is the problem as it slowly but surely increases in pressure over a four to six week period even when the heating is not in operation.
Mine started doing that about 4 years ago.  I did what my gas plumber said - disconnected the loop and blanked off the end and the open end of the switch/tap.  I reconnect every couple of years when the system needs a little top up.

Kim

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Re: CH Boiler running at too high pressure
« Reply #8 on: 29 October, 2017, 06:02:23 pm »
It constantly keeps topping itself up at a trickle as the fill loop doesn't close off properly.  It was a known problem with Vaillant boilers of our vintage.   We know that this is the problem as it slowly but surely increases in pressure over a four to six week period even when the heating is not in operation.
Mine started doing that about 4 years ago.  I did what my gas plumber said - disconnected the loop and blanked off the end and the open end of the switch/tap.  I reconnect every couple of years when the system needs a little top up.

Which is, AIUI, the spirit - if not the letter - of the regulations that are usually interpreted to mean that it's okay as long as a flexible hose is used.

Re: CH Boiler running at too high pressure
« Reply #9 on: 30 October, 2017, 10:12:28 am »
Bleed off some water from a rad so that pressure drops below red when hot. Check pressure when cold, write figure down.

Check it again when cold 24 hours later - it should be the same. If it has gone up, then water is trickling in via the fill loop as Polar bear described.

If cold pressure is constant but when hot it is going into the red, then either the pressure vessel isn't working, or air is getting into the system - both could be due to pressure vessel failing.
<i>Marmite slave</i>

Re: CH Boiler running at too high pressure
« Reply #10 on: 30 October, 2017, 06:55:49 pm »
Bleed off some water from a rad so that pressure drops below red when hot. Check pressure when cold, write figure down.

Check it again when cold 24 hours later - it should be the same. If it has gone up, then water is trickling in via the fill loop as Polar bear described.

If cold pressure is constant but when hot it is going into the red, then either the pressure vessel isn't working, or air is getting into the system - both could be due to pressure vessel failing.
I did this yesterday, bleeding off the rad in the hallway (as I can actually see the gauge while I do this - this is the only rad, btw, that I cannot fully rid of cold spots).
I reduced the pressure to the top end of the green area / bottom end of the black on the dial.
The upshot of this was that by this morning, the pressure had dropped sufficiently low that the boiler wouldn't ignite to give me hot water - never mind heating.
This evening I restored the pressure and ran the CH.
After about 10 minutes the pressure gauge had gone into the red, so I switched off.
Gary, the heating engineer has been summoned.
I hope it doesn't get too cold between now and Nov 13th when Gary is due to call. :(

Re: CH Boiler running at too high pressure
« Reply #11 on: 30 October, 2017, 07:23:07 pm »
Bleed off some water from a rad so that pressure drops below red when hot. Check pressure when cold, write figure down.

Check it again when cold 24 hours later - it should be the same. If it has gone up, then water is trickling in via the fill loop as Polar bear described.

If cold pressure is constant but when hot it is going into the red, then either the pressure vessel isn't working, or air is getting into the system - both could be due to pressure vessel failing.
I did this yesterday, bleeding off the rad in the hallway (as I can actually see the gauge while I do this - this is the only rad, btw, that I cannot fully rid of cold spots).
I reduced the pressure to the top end of the green area / bottom end of the black on the dial.
The upshot of this was that by this morning, the pressure had dropped sufficiently low that the boiler wouldn't ignite to give me hot water - never mind heating.
This evening I restored the pressure and ran the CH.
After about 10 minutes the pressure gauge had gone into the red, so I switched off.
Gary, the heating engineer has been summoned.
I hope it doesn't get too cold between now and Nov 13th when Gary is due to call. :(
Those are exactly the symptoms of an expansion vessel that is full of water, not half air, half water as the designer intended. See my post above about fixing it.
Quote from: Kim
Paging Diver300.  Diver300 to the GSM Trimphone, please...

Re: CH Boiler running at too high pressure
« Reply #12 on: 30 October, 2017, 07:57:04 pm »
Thanks Diver 300.
I've no doubt you are correct.
At present the system is 'limping / being fudged' to heat my HW and house.
You should take into account that I'm not sure how to take the cover off the boiler, let alone identify an expansion vessel (whatever that is).
My approach may change depending on the ambient temperature drop between now and November 13th when Gary the heating engineer is due to call   ;)

Re: CH Boiler running at too high pressure
« Reply #13 on: 30 October, 2017, 10:22:52 pm »
The expansion vessel is cylindrical, usually red, is often located outside of the boiler and google shows what they look like.

I'll admit that I hadn't considered the possibility that it could be difficult to find.
Quote from: Kim
Paging Diver300.  Diver300 to the GSM Trimphone, please...

Re: CH Boiler running at too high pressure
« Reply #14 on: 30 October, 2017, 10:37:59 pm »
We had similar symptoms at a holiday let. Fault was sludged pipe linking expansion to system. Having the CH  stat in the same room as the aga - and the impossibility of achieving any sort of balance prompted me to turn off the heating overnight. (We had of course  been instructed to leave well alone) Then it would not restart. The fitter spent over an hour clearing the pipe, which was  about 40 cm long and bike track  pump diameter with a piece of wire.

Aunt Maud

  • Le Flâneur.
Re: CH Boiler running at too high pressure
« Reply #15 on: 31 October, 2017, 07:15:44 am »
To avoid all this hassle, we bought a British Gas Homecare contract for £14 per month. We ended up getting all the guts including the heat exchanger replaced in our boiler over a period of two year,s and they nearly always came out the next day.

It was good value for us with two small children.

Re: CH Boiler running at too high pressure
« Reply #16 on: 31 October, 2017, 08:44:01 am »
The expansion vessel is usually red as described - but sometimes blue (I've fitted blue ones). On the top of it there will be a nipple covering a Schrader valve. If you press down the valve core, air should come out. If water comes out, the membrane has failed and you need a new vessel. If no air or a tiny bit comes out, you just need to connect a bike pump and add some air. It's that complicated!

But it sounds like there may be some other issues - the rad with cold spots sounds to be blocked up with debris
<i>Marmite slave</i>

Re: CH Boiler running at too high pressure
« Reply #17 on: 13 November, 2017, 10:58:23 am »
Heating engineer has been.
Expansion vessel was at fault. A bicycle pump was deployed to fix it.
The rad which wouldn't warm up had a stuck valve. A hammer was deployed to fix it.
Now we're toasty :)
The heating engineer has taken all of my money :(

Re: CH Boiler running at too high pressure
« Reply #18 on: 13 November, 2017, 02:44:53 pm »
Was it your bike pump? If so you should have charged for it!

Re: CH Boiler running at too high pressure
« Reply #19 on: 13 November, 2017, 03:05:48 pm »
Nope. Gary brings his own bike pump.
Zefal HPX.

Re: CH Boiler running at too high pressure
« Reply #20 on: 13 November, 2017, 03:16:00 pm »
Heating engineer has been.
Expansion vessel was at fault. A bicycle pump was deployed to fix it.
The rad which wouldn't warm up had a stuck valve. A hammer was deployed to fix it.
Now we're toasty :)
The heating engineer has taken all of my money :(

I sympathise.  I've also just handed over a large amount to have a £40 expansion vessel replaced.  Whilst I'll tackle some plumbing / heating jobs myself, it took two of them, a huge spanner, some WD40 and a little swearing to wrestle the pressure relief valve off the top of the expansion vessel before it could be removed from the wall.  Given the access, and the 20kg or so weight of a full expansion vessel, I'm glad I didn't tackle that one myself.  It was definitely a four handed job.

The defective expansion vessel was only 3 years old.  It may have been undersized, in which case the new one won't last long either :(

Re: CH Boiler running at too high pressure
« Reply #21 on: 13 November, 2017, 03:26:24 pm »
Gary is as surprised as I am that this boiler continues to give relatively trouble free service.
Other than a faulty diverter valve he's not had to do any work on it other than an annual service, and the last one of those he did was around five years go.
He fitted the boiler when I first moved in here.
That was in 2003.