Combi boiler turning ON-OFF-ON for hot water

psarinuk · 14 Jan 2008

Hi all

Happy New year first of all..

I bought a Ravensheat HE85(B&Q make I think) combi boiler in Feb 2006 and had it installed by a plumber who cannot be contacted at the moment..

The boiler has been running great since then but for the past 2-3 days, the boiler comes on for hot water but then turns off again within 15-20 seconds and then turns back on again after same time...

The tap is running at the same flow rate all this time, therefore, the water turns cold when the boiler turns off and then gets warm again when the boiler comes back.

However, I cannot be sure if the boiler is still going ON/ OFF in CH mode as radiators are still getting hot (I bled them as well).. This ON/ OFF behaviour matters more with HW as you need this constant temperature while taking the shower..

I am guilty of not having the boiler serviced since I bought it but I am planning to get that done ASAP. Could it be related to this?

Many thanks in advance for your help..

ChrisR · 14 Jan 2008

95% It's dirt in the secondary heat exchanger, collected from your dirty system. Extremely common.
Can be replaced or cleaned - do a Search

psarinuk · 14 Jan 2008

You could be right Chris.

I forgot to mention that I'd put some CH treatment/ cleaning acid from B&Q into the central heating system to get rid of any rust/ sludge/ dirt etc in Nov/ Dec 07.

I had it in the system for about 6 weeks after which I drained the central heating system about 10-15 times (followed the isntructions on the bottle).

Could this have any contribution to what you are saying?

Thanks for your input!

ChrisR · 14 Jan 2008

Could this have any contribution to what you are saying?

Not necessarily!
1) it's B&Q godknowswhat. Sometimes things get WORSE
2) the stuff would only go through the dhwhe when the tap's on - not much.

psarinuk · 14 Jan 2008

2) the stuff would only go through the dhwhe when the tap's on - not much.

Sorry but what does dhwhe stand for? Is it secondary heat exchanger?

Could I check the sec heat exchanger myself or would I need to call the plumber?

Cheers..

ChrisR · 14 Jan 2008

Domestic HW h/ex = secondary heat exchanger
A boiler man might clean it, probably wanting to replace it.
A plumber probably wouldn't have a clue.

A lot of each would tell you you need a new boiler.

You can DIY if you read up.

psarinuk · 14 Jan 2008

Right, I've removed the front cover and side covers. I've also removed
the main cover, then the flue hood underneath it.

I've come to a point where I need to remove the fan assembly as said in service instructions...
I;ve removed the electrical connections for fan motor..
The fan assembly seems stuck into the condensing heat exchanger (which I assume is same as secondary heat exchanger)...
There is some rust type yellow material blocking the fan from the aluminium pipe of exchanger. Can't see any screws and don't think I've missed any..

The fan then also needs to be withdrawn from the appliance but it seems firmly stuck..

Any ideas how to remove the fan. Its a Ravenheat HE85 T combi boiler...

Also just to keep the boiler running, I put the electrical connections of fan back into place but now the boiler is not firing. Instead the overheat red light is coming up when I try to run mains water... Is it due to flue hood being disconnected?

Plz Help!!

psarinuk · 14 Jan 2008

Plz see if anyone can help me. I've phoned a few boiler servicemen but none are available till Wednesday.

If there is any info missing in my description, please let me know..

tabs · 14 Jan 2008

psarinuk said:
Is it due to flue hood being disconnected?

Plz Help!!

Yes, it is.

At last if you reassemble the boiler you will have heating. Hot water can be obtained from other sources, you can survuve a few days without it direct from the boiler. Its one reason I always have an electric shower installed as well.

bengasman · 14 Jan 2008

psarinuk said:
I bought a Ravensheat HE85(B&Q make I think) combi boiler in Feb 2006 and had it installed by a plumber who cannot be contacted at the moment..

You can find his CORGI number and address on the commissioning report, and check his new phone number on the CORGI website.

As for the dhw problem, powerflush will solve the problem, replacing the hex is about as useful as buying a new tyre when your drive is full of nails.

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Combi boiler turning ON-OFF-ON for hot water

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