Gloworm Boiler Lock-out

[DIYSB]

Had a problem for a couple of months now and tried everything I can think of without success. I've been told the symptoms are know as Boiler Lock-out.

I have a Gloworm15hxi boiler and the problem is that it works fine when there is a demand for CH and HW or just CH but when there is just a demand for HW it shuts down very quickly. I have replaced the pump as part of maintenance programme and have now also replaced the Honeywell Y Plan diverter valve and powerhead unit. Upon inspection of the old valve it appaeared to be in good order and was working properly. I also replaced the themostat on the hot water tank just in case that was the problem but still the problem persists. There is a by-pass valve around the 3 port valve and that hasn't been touched and is fully open.

The problem only materialised after the summer when the demand for CH began. Before theat it had been working fine with just HW being supplied by the boiler. I've had it serviced and its working ok. I'm not a plumber or gas fitter but do most of my own plumbing jobs (leaks,taps, radiators etc) but would never go anywhere near gas.

So I'm scratching my head as to what could be causing it and was hoping someone here might be able to give me some suggestion?

 

[Blake]

Hi,

The bypass should not be fully open, turn it all the way off and then crack it open a fraction.

 

[DIYSB]

Hi,

The bypass should not be fully open, turn it all the way off and then crack it open a fraction.

Thanks for the prompt reply mate, will try that now. As I said, the by pass valve is open but in the same position as it was before the problem started. Will let you know how I go on.

Thanks again - appreciated.

 

[Blake]

When there is a demand for HW only, does the water get hot enough? If the boiler is overheating and locking out on HW only, is could be an air lock or partial blockage of the coil in the cylinder. You may find that the boiler locks out even quicker when you return the bypass to the correct position if there is an issue with the coil.

 

[DIYSB]

When there is a demand for HW only, does the water get hot enough? If the boiler is overheating and locking out on HW only, is could be an air lock or partial blockage of the coil in the cylinder. You may find that the boiler locks out even quicker when you return the bypass to the correct position if there is an issue with the coil.

The water doesn't get hot when there is just a demand for HW because the boiler shuts off almost straight away. Temperature in the boiler rises quickly, gas burn tries to regulate but it shuts off because the water in the boiler reaches and tries to exceeed the set temparature. When the CH is on as well as the HW, the HW gets hot enough and it works perfectly.

I checked the by-pass valve again and it wasn't fully open as I said (was wrong about that) but it was open about half a turn.

I did wonder about an air block and was thinking of draining some water off the return pipe from the bottom of the water tank flow return pipe where there is a drain valve but I've already checked the flow and return pipes to the coil in the tank and they are both hot, so I think the water is flowing ok.

I replaced a rad in the summer and the problem only seemed to come after that which made me wonder about an air block but I've drained the system twice since then to replace the pump and the diverter valve and I've done it many times before without any problems with air blocks in the hot water pipes.

I'm wondering if it could be a problem with one of the thermistors in the boiler on either the flow or return?

 

[DIYSB]

Checking this further there seems to be a strange sequencing thing going on. When I shut the entire system down electrically and turn it back on asking only for HW it works ok. When I then demand CH as well as HW it work ok but then when I shut the CH off and leave the demand for just HW it shuts down. The burner gets louder and the temperature in the boiler rises until it shuts off.

 

[Blake]

Well I'm afraid I can't help with the boiler itself as you will need to get a GSR engineer in to take a look. But the fact that when only on HW only the boiler overheats and cuts out, suggests to be that you have a flow issue around the HW cicuit. Does the pump run when only in HW only?

 

[DIYSB]

Well I'm afraid I can't help with the boiler itself as you will need to get a GSR engineer in to take a look. But the fact that when only on HW only the boiler overheats and cuts out, suggests to be that you have a flow issue around the HW cicuit. Does the pump run when only in HW only?

Yes the pump runs in all situations. Baffling really because I don't think its the boiler as it works fine with HW & CH.