combi boiler - multiple issues

4 Jan 2011
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United Kingdom
hello all,

first time poster. i've read all the boiler FAQ's and searched the forum but haven't found an answer to my problem. can anyone help with the following:

i had an issue last winter whereby the HW would come on, heat to max. temp. then turn off again. after 10-15secs this cycle would repeat until the tap/shower was turned off.

i was only living at the house intermittently at this point, and when the cold weather went the HW operated normally so I didn't get it looked at.

over the last month or so, this problem has returned and is now so bad that i get maybe 10secs of hot water in a 3-4min. period. same as before - HW kicks in, ramps up to max temp. then goes off again.

along with this, the CH circuit is playing up. no matter what temperature it is set at the boiler will only fire intermittently for 10-20 secs then it will go off again. a red light on the panel flashes when it isn't firing but i've yet to find the manual to discover the meaning of this.

i spent xmas away so am only just getting round to diagnosing/fixing these issues. i installed the full GCH system myself [apart from connecting the gas and comissioning the boiler] so i want to fix it without resorting to calling in a plumber. i just need a checklist of things to sort through to identify the problem. colleagues say divertor valve, pump or heat exchanger, but that's hardly a narrow field to work with!

reading the other boiler threads, i'm going to start this evening by looking at the divertor valve, but feel free to ask me questions to help diagnose the issue.

boiler is approx. 3yrs old, i *think* it's a baxi but i'll hunt the manual tonight and confirm the make/model in the morning.

cheers in advance.
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max temp. as in whatever it is set at.

after turning the house upside down, i found the manual! the flashing light sequence corresponds to a faulty air pressure switch. i took it off and brought it [and the manual] to work an intend to have one of our controls people test it here or lend me a multimeter to do so en situ.

i'm not 100% convinced its just the switch as it worked all spring-autumn with no issues, but at least with the manual and all the covers off i can sort it quickly and cheaply.

PS - boiler is a Biasi Garda HE. Not the best it seems but hey ho.
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We dont give advice on an open forum on gas or combustion issues and that includes safety devices associated with the combustion process.

We dont advise any DIYer to open the combustion chamber. If the fault were there you need a gas registered engineer.

I any case I dont expect it to be an APS fault on that model. It surprises me that you dont realise the importance of quoting the full model and serial number.

Apologies for lack of full info, as I say I am new here.

The full details are:

Biasi Garda HE: M96.28SM/B2
G.C. Appl. No: 47-583-04A

Pressure switch is a Honeywell C6065FH1185:2 [1.38mbar]. I have found these for circa £40+VAT/DEL.

I appreciate what you're saying from the safety point of view, but it's a 2 second job to change - 2 wires and a tube. I can borrow a gas detector if needed and there are combustion engineers on site I can speak to, but I've no qualms about doing this myself.
It may be a two second job for you but that does not mean that you should be doing it.

Get one of those combustion engineers to do it. But I dont expect it to cure the fault.

Being new does not mean that you should not read the rules and give full information on the boiler. I still dont know the serial number which I asked about.

Again, apologies, I read the FAQ's but not the rules. I take it you mean the boiler serial no? I don't have that to hand at present, just the manuals, parts list and the faulty switch.

TBH, I'm not convinced it will fix the fault either, but that's what the boiler says it is. It's a start anyway, and I have now found one for £14 + delivery so an inexpensive one at that.

In your experience, what do you think it might be?
In my experience you need a registered engineer who can check gas and combustion issues!


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