Combi boiler problems - several strange issues

[bradleyd]

I have a ICI Caldaie Solar I 20 SE comvi boiler here, it was fitted when the house was built 10+ years ago.

It provides hot water on demand to taps in kitchen and utility room. Hot water for all other rooms is via a hot water cylinder heated via timeclock.

On Saturday I found there was no hot water in the bathroom. Went down to the boiler and turned the timeclock to 1hour immediate heat........still no hot water.

I discovered that when told to heat the storage cylinder the boiler will fire and run for about 30 seconds and then shutdown (but pump keeps running longer).

Then I decided to check the central heating - it doesn't even start the boiler and instead I heard fast clicking from near the boiler - wired between the boiler and the wiring centre was a relay and when the central heating is on at the timeclock this relay continually toggles (opens/closes).

Think it was just a faulty relay I got a replacement one today but it is behaving in the same fashion.

So I'm not sure if there are 2 distinct problems or just 2 effects of a single problem:

- when timeclock told to heat water in storage tank boiler runs for approx. 30 seconds and then stops
- when timeclock told to heat radiators the relay toggles continually and the boiler never tries to start.

Since then I have noticed that if I run the hot tap in either the kitchen or utility room then the boiler will fire and run no problem to heat these taps on demand.

So then I tried turning on the hot water storage at the timeclock while I had the kitchen tap running (and so the boiler was running) but I didn't feel any of the pipes leading to the storage tank get hot.

Likewise I tried turning on the central heating while the kitchen tap was running and again no heat on the pipes to the radiators.

I'm guessing that the problem is internal to the boiler (rather than a problematic motorised valve for example) as when I left the kitchen tap running (and so the boiler was going) and also put on both hot water storage and central heating the only pipe leading out of the boiler that was hot was the seperate one for the on-demand taps.

I'm interested in any suggestions (especially as why the relay is continually toggling when central heating is on).

 

[Agile]

Your boiler is not a very common one in the UK.

It seems you have a combi supplying the kitchen and a storage cylinder supplying the bathrooms.

The boiler works fine in combi mode.

I have no idea what your relay is or does as you have given no clues.

Almost certainly the problem will be with the external controls circuits.

Tony

 

[bradleyd]

It seems you have a combi supplying the kitchen and a storage cylinder supplying the bathrooms.

The boiler works fine in combi mode.

Yupe

I have no idea what your relay is or does as you have given no clues.

Almost certainly the problem will be with the external controls circuits.

As far as I can tell the timeclock has 2 wires to signal for storage cylinder heating and for central heating, these wires then go into a wiring centre (i.e. patch panel) and then go to the relay which then goes to the boiler. So the timeclock drives the relay which drives the boiler.

If the problem is due to external controls then why does the boiler shutdown after approx. 30 seconds when told to heat the storage cylinder? The "replacement" relay that I tested today has a LED to show when its circuit is closed and it stays lit the whole time the timeclock requests storage cylinder heating yet the boiler goes out after 30 seconds so (in this situation) this makes be think this particular issue is within the boiler............whereas the toggling relay when central heating is required does sound more like an external problem - but the only external controls are the timeclock, the hallway thermostat/cylinder thermostat, and the relay.

 

[mysteryman]

There must be either a diverter valve [Y Plan] or pair of 2 port valves [S Plan]somewhere. This is because the central heating side of your boiler is set up like a conventional boiler-plus-hot-water-cylinder layout.

You need to identify these items and troubleshoot them. FAQs may help.
Or the problem could be that the boiler is not responding to what it sees as a central heating demand. That could be a sticking diverter in the boiler.

All the ICI boilers I ever saw had a diaphragm operated diverter which was heavily spring loaded into the central heating position, but they can stick in the hot water position.

Probably your best course is to simulate a CH demand at the boiler to see if it fires up and pushes heat out from the CH flow., if not, open any motorised valves manually and try the boiler again. Keep on in the direction of your radiators and hot water cyl until you find the fault.

The other possibility is that the separate DHW cyl is immersion heater powered only. It would be pretty daft, but who knows?

 

[bradleyd]

There must be either a diverter valve [Y Plan] or pair of 2 port valves [S Plan]somewhere. This is because the central heating side of your boiler is set up like a conventional boiler-plus-hot-water-cylinder layout.

Yupe, its a S Plan layout - there are 2 motorised values below the boiler - even when I managed to get the boiler to fire and stay running (by running the tap in the kitchen) and then turned on the hot water and/or central heating on the timeclock I didn't feel any heat in the pipe leading towards these motorised valves, so even if they were faulty (which I don't believe as I can hear them close when I then turn off heating/hotwater) I would expect the pipe leading towards them to get warm.

All the ICI boilers I ever saw had a diaphragm operated diverter which was heavily spring loaded into the central heating position, but they can stick in the hot water position.

I found the installation manual for the boiler online here: "http://www.icicaldaie.co.uk/manuals/boilers/Solar%20I20SE%20Installation%20Manual.pdf" and there's no mention of a diverter in the schematics (page 37).

Probably your best course is to simulate a CH demand at the boiler to see if it fires up and pushes heat out from the CH flow., if not, open any motorised valves manually and try the boiler again. Keep on in the direction of your radiators and hot water cyl until you find the fault.

This is basically what I've been trying to do........if the pipe from the boiler for CH flow never gets warm then is a problem with the motorised values still likely to be a factor?

Thanks everyone for comments/advise.

 

[DP]

You boiler is a combi boiler that is also used to heat a cylinder which in turn supplier hot water to the 'bathroom' areas.

Running the hot water tap in the kitchen and expecting the heating pipe to get hot will not happen as boiler mechanics are in 'hot water' mode.

I suspect when you run CH or HW (cylinder), boiler temperature rises rapidly and then boiler shuts down.

For S plan you do not need a relay. Terminal TA when closed and selector knob on front panel (selecting winter setting) would normally supply heat to radiators.

Is the selector in heating mode?
Have you checked the pump is running when heating call is active?
Have you removed the wires from TA and shorted the terminals to see if the boiler runs?
Have you checked the timer wires that go 'hot' when CH or HW is ON?

I do not see the need for relay if you have an S plan (this sundial plan uses two two port valves). End of travel auxillary switch would do what the relay is doing at present. You have already said the LED on new relay is ON indicating relay is powered and relay contacts will be closed (TA shorted to run boiler)

I would initially be looking at the pump, then be investigating the need for relay inclusion.

 

[bradleyd]

I would initially be looking at the pump, then be investigating the need for relay inclusion.

I had a guy out to have a look today and there were 2 distinct problems:

- when HW was on to heat the storage cylinder the pump wasn't working (was stuck) so that was quick to fix

- when CH was on at timeclock the relay between wiring centre and boiler was clicking on/off repeatedly - turns out that the relay makes a connection (TA terminals?) on the boiler to turn it on, the relay is fed by a combination of sense wires in both the motorised valves and the sensor in the CH value was faulty, the value would open but the signal to indicate this was intermittent and so caused the relay to chatter. Solution was to replace the motorised value head with another one and bingo CH works as expected.