Gas Valve Settings

[robflh]

My Baxi Platinum 28 HE (47-075-21) has had the following fitted. Refurbished main heat exchanger, refurbished PCB, new electrodes and a second new gas valve. The boiler is back up and running but the gas goes off as it gets near the temperature the central heating has been set to and then the gas repeatedly goes on and off until the boiler gets to the set temperature and then the gas goes off until the temperature has dropped enough for the boiler to fire up again. The cycle repeats continuously until the thermostat in the living room turns the boiler off.

My GAS SAFE REGISTERED ENGINEER thought it could be a faulty CH NTC sensor but if I turn the hot water to the lowest setting I get the same problem.

I cannot remember what he set the high to apart from the fact it was within 8.7 +/-0.2 however the low is 8.3 which is on the low side but within tolerance 8.4 +/- 0.2. Before I get my GAS SAFE REGISTERED ENGINEER back and have him set it to 8.5 or even 8.6 which will hopefully sort out the problem does anyone know if there is anything else that could cause the same problem?

 

[oldbutnotdead]

Blocked pipe, failing pump? What's the boiler temperature set at- does adjusting it make any difference to the cycling?

 

[ianmcd]

My GAS SAFE REGISTERED ENGINEER thought it could be a faulty CH NTC sensor but if I turn the hot water to the lowest setting I get the same problem.

What you call a CH NTC, is a system NTC and it will over ride everything apart from High limit NTC and flue NTC , if the system gets too hot it doesnt matter what your HW NTC says

 

[robflh]

What you call a CH NTC, is a system NTC.

does adjusting it make any difference to the cycling?

Increasing or decreasing the CH temperature makes no difference; it still cycles but the hot water works fine at 55 degrees.

I have some x800 but I would like to put that in the sysytem for a couple of weeks in a few months time.

CH NTC is what he called it, which slightly confused me as it is in the same pipe for the central heating and hot water.

Am I allowed to close the valves for the feed and return under the boiler, drain the boiler down and change the system NTC. I would also like to check the pressure vessel is at 1 Bar at the same time.

 

[Madrab]

I have some x800 but I would like to put that in the sysytem for a couple of weeks in a few months time.

Don't leave X800 in for that long, it can damage your system if left in for that amount of time, X800 should be left in for hours not days.

X400 is the one that can be left in for weeks.

I believe the NTC sensor is in behind the combustion cover so as a DIY'er then no you shouldn't really be in there.

 

[gas112]

Boiler sounds like triggers broom . Setting the gas valve to exactly 8,7 and 8.4 from what you say it is set at already will not have any effect whatso ever on what is happening to your boiler

 

[ianmcd]

DO NOT use X800 or you will have a lot more problems than you already have

 

[robflh]

DO NOT use X800

Never ever use it or use it for a few hours? My system only has six radiators and each of them is connected to a manifold with 8mm microbore.

The manual for my boiler does not call it a system NTC. Page 8 item 25, page 57 section 12.10 and page 44 Wiring Diagram.

http://www.gasapplianceguide.co.uk/Baxi_Platinum_Installation_Guide.pdf

Don't leave X800 in for two weeks, it can damage your system.

Someone that should know better said to put it in for two weeks, well that is what I think they said but as the maximum time in a system is 20 hours even two days whould also have been too long. So now I am not sure what they said.

 

[robflh]

The Gas valve was re-adjusted last week and with the low set to 8.6 the boiler is working properly.

Using the X800 for 8 hours or the X400 for a few weeks I will need to flush the system and get rid of any chemicals and sludge. My Baxi Platinum has a 22mm blanking plate underneath it for the feed pipe and a 15mm plate on the return pipe.

If I turn off the feed valve, return valve and all the radiators valves except a small radiator downstairs, I can drain the water out of that radiator and the 8mm microbore pipes taking the water to each radiator via a manifold.

With that done I am hoping I can remove the 15mm blanking plate and fit a 90 degree 15mm to 10mm compression reducer and a 90 degree 22mm to 10mm reducer on the feed pipe.

I can then close the drain valve remove the hose pipe from it and then connect one end of it to the return under the boiler and put the other end in an outside drain. With the garden hose fitted to the 10mm feed connection I can turn the outside tap on and have water going to one radiator via the feed pipe and coming back and in to the drain via the return pipe.

Once I have clear water going it to the drain I can turn off the tap and both valves on the radiator I have just cleaned and open the valves on the other downstairs radiator and repeat the process. Having flushed all the radiators I can swap the two hosepipes under the boiler and reverse flush each radiator.

Lastly making sure all radiator valves are closed and opening the valves under the boiler for the feed and return I can flush and then reverse flush the boiler.

 

[Madrab]

Can I suggest that you are very careful, flushing a 8mm piped system is fraught with risk.

I have experienced more issues when flushing an 8mm system than any other purely down to the narrow bore of the pipe. If any large pieces of crud that are attached to the larger pipework or in the rads gets into the microbore and gets stuck you can make the system much worse.

Only way I'll try to clean a microbore is to remove the rads, clean them outside and reverse flush the pipework from each rad valve, that's to minimise the risk that any solids in the system doesn't get into the 8mm pipe. That's after trying to convince the client to not bother and replace it all.

There is always a caveat written into any flushing/cleaning of a Microbore system.

 

[ianmcd]

@Madrab reminds me of on a job with a very good mate , really good heating engineer he had made this contraption up for clearing blocked 8mm pipes it was basically a holding air vessel with a valve on, he would pump the little vessel up to 6 Bar air and open the valve and it would push all the crap in the pipe back to the manifold, we were on a job and he went up to the loft to remove the bungs , he shouted me up , the complete loft was absolutely covered in black shoite, but the rad started working, we got paid and done a runner

 

[robflh]

I have experienced more issues when flushing an 8mm system than any other purely down to the narrow bore of the pipe. If any large pieces of crud that are attached to the larger pipework or in the rads gets into the microbore and gets stuck you can make the system much worse.

I replaced the old twin entry rads with double panel double fin rads about three years ago. So hopefully there are no large deposits in them. Over the years the system has had X400 in it from time to time. Before I put a bottle of X100 and X200 in the system I want to give the whole system a quick clean.