Help please!Boiler pressure rise & fall,reset.Pipe leak?

6 Jan 2010
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United Kingdom
Please help, am in desperate position, no heating, extremely worried.

Potterton Lynx 2 combi just had annual BG service after insurance renovation work in basement flat because of 'Escape of Water' damage from rising main. The system had been in full working order at time of investigation of leak which turned out to be rising main (not central heating related, which was tested at the time, good sustainable pressure, about 1.5 bar).

All radiators had been removed to repair rising damp/rot in walls and floors, one replaced in the bathroom, 21mm marine ply subfloor and expensive 21mm hardwood floor laid on top throughout flat.

During refitting of radiators, 2 had leaky valves which were fixed, but the system was not checked as fully working before contractors left or before the hardwood floor was laid by another company.

Within hours of the boiler service (after the floor was laid!!!), system cut out to 0 bar pressure, no heat no water, even on reset.

Second BG engineer refilled system at filling loop, replaced ISO valves which had slight dripping leak (left them in permanently open - vertical - position), fitted new ignition lead which had corroded, left the pressure at 1.5 bar, boiler cut out within hours.

Third engineer checked pressure release valve, dismantled it and flushed it through (no problem), replaced expansion vessel (which was full of black gunk), was going to change coupling loop but toby outside is seized in this perishing weather so couldn't isolate water supply in the flat.

B Gas say boiler is on 'restricted parts' but still serviceable within their Homecare 200 plan, even though third engineer got me to sign Safety Warning saying 'Boiler/Kitchen/Terminal Position' !!!! I assume that means it's becoming too expensive for them to service or find the fault, even though I've been paying up for 8 years and no call outs.

Kept an eye on the pressure gauge and it steadily rises to 2 bar then boiler shuts off and I have to reset every 40 minutes. All radiator valves at high, all bled, all dry at the valves (no leaks above floor), all heat up very quickly and no cold spots at bottom or top.

Last engineer suggested magiclean flush of system, or maybe there is a subfloor leak, maybe a floorboard nail or screw only slightly lodged in a pipe.

Question: are there any other things that could be going wrong in the boiler to go to high pressure, shut off, then reset light come on? If I don't reset, it eventually goes to Low Pressure warning light and 0 bar on gauge; same when it is switched off.

I seriously don't want to lift this floor and subfloor again to find possible leak, an insurance nightmare on top of an already 7 month insurance and botched jobs nightmare. There have been three main contractors on the job, two of whom have worked on the radiators and valves, but any one of many workers could have accidentally lodged a nail or screw sub floor into pipes, or it could be a slow leak at the new bathrooom radiator valves which were sectioned on sub floor.

Surely, this must come under Accidental Damage within the existing claim on Buildings Insurance which is already picking up the bill for the original repairs? There has been only one 5 minute visit from a Contract Manager at the beginning of stripping out work (no central heating pipes were replaced or lifted).

I can see this getting bogged down by the Loss Adjuster in legal claims about liability when all I want is my flat back with the working Central Heating System it had at the outset!!!

Please tell me it might still be the boiler. Thanks, and sorry for long post.
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Its difficult for me to come to any conclusion from what you have written.

The reality is that all the people you have had will be lower calibre who are expected to only spend a short time with you.

Another reality is that you clearly are not expecting to pay any money to get it sorted. The result of that is that you are stuck with the BG cover. All you can do is repeatedly complain un til they get so fed up they send a more senior person. What you will get is a promoted engineer but probably not someone who is very good at diagnosing anything which is a little different.

I would be happy to come and diagnose all the problems but you would have to pay the cost of about a years of BG cover plus travelling costs. I dont think you would want to do that.

Today, started from scratch with system off, 0 bar on pressure gauge, did NOT top up system at coupling loop!

Mains electric at wall switched on, timer set to ON, boiler switched on to 24 hours, Low System Pressure Light came on and boiler wouldn't fire even on drawing hot water.

I gently pushed the control panel dashboard, oval soft grey plastic area, and noticed the Low Pressure Light flickered and went out. Next, holding this panel in with trepidation the Demand and Ignition lights came on. Put the boiler setting to almost max and hot water to mid, and drew hot water which teased Ignition to Flame and boiler came to life.

Could hear water gurgling around the boiler and the flow pipe getting warm, still worried it might explode if Low System Pressure warning is infact correct. After about 30 minutes all radiators were hot and pressure gauge had steadily risen from 0 bar to a comfortable 1.5 bar.

Hallelujah, I thought. Surely this means the pcb is dodgy if it takes a gentle push to bring its operational red lights to life? Surely there must be a loose connection in the electrics giving wrong information to the firing up process???

On the other hand, why was the boiler starting out from cold at 0 bar pressure. I thought in a closed system the pressure is constant on the gauge whether the system is on or off?? Please advise.

For a moment I thought the pressure gauge is broken, but then why would the pressure rise to normal range once the system became operational?

So there was heat in all rads while the boiler was firing and it managed a couple of cut outs and self ignition for temperature control, steadying at about 1.5 pressure.

Rising to about 1.8 bar the boiler started to whine like a tortured seal then clicked to Reset light beside control dashboard panel.This repeated itself, boiler building up to very loud whine then stops firing, reset light back on again (about every 30 minutes), held reset button in for about 10 seconds, and tease it back to firing by drawing water. Before these resets the pressure gauge was falling down towards 1 bar, and inevitably to 0 bar. Occasionaly, I could get the boiler to go to Demand and Ignition; I could hear the pilot flicking wanting to ignite but it wouldn't until I drew water.

Since I am having to reset every 30 minutes, preceded by very loud whining noise, all is not correct.

For peace of mind that I don't need to rip up an entire flat of hardwood and subflooring to find an elusive leak, do the facts of what happened today with the pressure suggest the fault is in the boiler and not in the pipe work?

All help welcome and hugely appreciated. Are BG just trying to panic me and sell me a new boiler which, I admit, is getting on at about 10 years old?

My main concern is to be certain this is a boiler problem and not a nail or screw bedded in a subfloor pipe, slowly taking the pressure off. Surely, the fact I got it up to 1.5 to 1.8 bar before Reset, and the obviously dodgy pcb which works when you press upon the panel is positive, even if this is not perfect.

If it is the boiler I will take the pipe leak as scaremongering, and press ahead with BG to repair the boiler (available parts allowing). This will be a huge relief, even if I have to buy a new boiler. I am not prepared to do that if there is any possibility of a leak since my only recourse is to see if I am covered under buildings insurance for lifting and relaying of all floors again, way too much money and stress.

Can anyone rest me assured the pressure and continual reset problem is in the boiler, and not a leak in the pipes, and explain why?

Thanks Tony. I don't mind coughing up for a new boiler out of my own pocket, but not if there's an insurable leak under a hugely expensive new floor.
The pressure is rising because the expansion vessel is not operating to adsorb expansion.

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But the engineer fitted a new expansion vessel last week? Does pressure in the system eliminate the probability of leaky pipes? Would a leak not mean permanently low or decreasing pressure on every fire up?

Is there a fix for the expansion vessel not operating to absorb expansion?

What do you make of the pcb, where a gentle push lit up all the ignition settings and the boiler fired?

Again, many thanks.
BG engineer booked again for Saturday.

Would welcome any questions I should ask him. For example, how can I prove pressure problem is in the boiler and not the pipes? Why is the pressure gauge settling at 0 bar when system is switched off? It must be potentially dangerous to keep resetting it every 30 minutes and teasing the boiler to Ignite by DHW .

A new pcb seems a good idea, but why is the boiler rising from 0 bar to about 1.8 then cutting out to reset every 30 minutes? If the boiler is overheating, then are the CH and DHW Overheat Thermostats needing replaced? What about the Water Pressure Sensor or Water Temperature Sensors, or the CH and DHW Water Flow Switches?
My simple conclusion is that the communication pipe between the boiler and the expansion vessel is blocked.

Many BG engineers dont seem to know how to diagnose that.

Its a common fault on the later Potty Puma. I dont remember exactly how thats arranged on the Lynx II. But your description of the problem indicates thats whats wrong.

Its actually very simple to prove that with an air pressure gauge on the EXV.

Pushing the PCB is apparently creating a bad connection which prevents the low pressure switch from stopping the boiler from running. Nothing very exciting about that.

The reality is that all the people you have had will be lower calibre who are expected to only spend a short time with you.

Like that one :LOL:

OP listen to Tony he is not a numpty like some BG guys
Thanks Tony, really appreciate your reply. Will mention communication pipe between boiler and exp vessel to BG.

Whether the pcb is faulty or not, should the pressure gauge still fall to 0 bar when the system is off?

I thought water pressure in a combi closed system stayed constant on the gauge, boiler on or off?

Is that not how you know to top up the system every 3 months or so when working normally because there is usually a slight drop, say from 1.2 bar to 1 bar.

BG are determined to say I should rip up my new floors and hunt for a nail or screw leak subfloor. This is a basement flat with a concrete screed, the pipes protected by wooden battens, no underfloor joist area to crawl about underneath, so entire floor would have to be scrapped!

I'm not sure BG don't want to allocate time to eliminate all possible boiler problems, but they must be losing money on all these recalls. Well, I have paid up for eight years and no call outs!

Potterton Lynx 2
The PCB has no bearing on the pressure reading!

On Page 22 the flexible hose going nowhere under the word "pressure" is blocked!


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