Combi boiler issues

RikRaccoon · 8 November 2013 at 11:19PM

Wondered if someone may be able to shed some light...

I have a combi boiler - a Winchester Bosch Highflow 400. We bought our house last year, and noticed that the radiators in two of the rooms weren't working. There were plenty of other things to worry about though, and a month later (still no heat in those rooms) the boiler cut out. The issue was simply low pressure, so I opened the valve on the filling loop, and the boiler came back to life - and the radiators in both rooms suddenly were heating up like all the others in the house. That lasted through the whole winter/spring, but now, we've got the same problem again. I almost want the system to lose pressure so I can start it up again like last year. Does anyone know what may be the problem? I've tried bleeding the rads, and all that comes out is slightly green water. Any ideas how to fix, or does it need a professional to take a look?

Thanks in advance for any help and advice!

diywhynot · 9 November 2013 at 4:29PM

Time for a service. Tell the RGI about the problems you have before he/she attends.

ollski · 9 November 2013 at 8:01PM

Its a long way from winchester to worcester!. Still not sure on the current problem, has it cut out? or do you just have a couple of cold rads?

RikRaccoon · 9 November 2013 at 10:01PM

Sorry it wasn't clear.

So I had two cold rads in 2012, boiler conked out, repressurized, everything worked (no cold rads), worked until Spring 2013 when we turned the heating off for the summer.

Now this year, back to two cold rads.

Service sounds sensible - it was just that the problem solved itself last time, plus it is an odd situation and wondered if anyone else had experienced similar.

RikRaccoon · 9 November 2013 at 10:02PM

ollski wrote: »

Its a long way from winchester to worcester!. Still not sure on the current problem, has it cut out? or do you just have a couple of cold rads?

Yes - Worcester... not so far away!

ollski · 10 November 2013 at 8:56AM

If it's just two cold rads try turning off all the other radiators and run the heating with just those 2 on, when they start getting heat through them turn the others back on.

macman · 10 November 2013 at 10:34AM

Where exactly in the house are the two rads that are cold? Top floor, ground floor? Are they cold all over or just at the top/bottom?
If the DHW side of the boiler has been working OK once adequately pressurised, then it doesn't sound like a boiler problem. You may have a leak or blockage/sludge on the CH circuit

RikRaccoon · 11 November 2013 at 12:52AM

macman wrote: »

Where exactly in the house are the two rads that are cold? Top floor, ground floor? Are they cold all over or just at the top/bottom?
If the DHW side of the boiler has be working OK once adequately pressurised, then it doesn't sound like a boiler problem. You may have a leak or blockage/sludge on the CH circuit

It's a bungalow, so ground floor. Cold rads are cold all over. The pipes leading to them are also cold. DHW is working fine. I bled the rads and green-tinged liquid came out - is this a sign that the water isn't flowing through them properly? Water wasn't dirty, but distinctly green. Is sludge a DIY-able problem? What are the possible solutions?

Thanks for all the help so far - is much appreciated.

macman · 11 November 2013 at 8:31AM

OK but are the two rads in sequence on the CH circuit, i.e. two adjacent rooms?
Yes, you can flush yourself, though it can be a messy job. Powerflush will require equipment hire.
But since the service is due anyway, why not get your RGI to advise when he does that?

vm2pensioner · 11 November 2013 at 9:25AM

I have had similar problems in the past. Sometimes it's just a thermostatic valve sticking shut. However, with 2 rads sounds more like a circulation / airlock issue - are the affected rads at the end of the circuit? Try shutting off all the other rads, see if the cold rads then heat up, open other rads again and then re-pressurise the system, if necessary. Worked for me with a combi.

matelodave · 11 November 2013 at 11:17AM

If its green then it's probably got an inhibitor in it - usually the water is black and horrible. You should be able to isolate where the problem is by turning all the rads off, and then on one at a time and making sure that they all heat up individually. If one or more don't it may be that it's a sticking rad valve, someone has been fiddling or there's a blockage or air lock in the plumbing feeding those two rads, in which case a more detailed check or flushing might be required