Our house has a Veissman Vitodens 100-W gas boiler along with a solid fuel cooker that can also provide hot water once it reaches temperature. As a result, we have this H2 Panel that controls the hot water system in our airing cupboard upstairs. 

The system is gravity fed from an F&E tank in the loft with one circulation pump moving the water into the hot water cylinder whenever its thermostat calls for heat (setpoint 55°C). The H2 panel automatically turns on the boiler when its needed. When the timer asks for the central heating, the panel will activate a valve to supply flow to the rads.

Something went wrong int he middle of the night a week ago when the pipes started making banging noises. These bangs happen whenever the solid fuel cooker is on and reaches temperature (58°C) and the panel switches the supply from the boiler to the solid fuel cooker. Obviously, we haven't been burning any coal for the last couple of months so I was confused but it did stop.

What resulted is the HW cylinder asking for a top up ever since yet it never reaches temperature. The gas boiler didn't throw up a fault but it was turning the burner on and off by itself so the supply is never constant. Our hot water has been quite warm, hot to the touch but not hot enough to cause any pain though. The pump started making a whirring, gurgly noise so I bled it. No change there. Eventually I straight up replaced it with a new Grundfos and it still made the same noise. Another symptom was no flow reach the radiators. The 3 port valve works as the pipe at the panel gets hot but none of the radiator's inlet pipes get warm despite making sure they're all bled.

A couple days later I rang up the company who designed the H2 panel (Mill Cottage Plumping, formerly Heating Innovations Ltd, [www.h2panel.co.uk](http://www.h2panel.co.uk/)) and after describing the symptoms, has was confident it's the 3 port valve that controls the supply between the boiler and the cooker. I swapped the whole thing over but I couldn't find like for like so I got a newer 5 wire model to replace the old 3 wire model. Wiring issue will be mentioned later.

After replacing the valve, filling the system back up and bleeding the air out as much as I could (including rads), the motor was sounding smooth which was great. Flow was reaching the radiators as they got warm but that's as far as I got. The boiler was still not staying on constantly to provide a supply of hot water to fully heat up the HW cylinder.

The boiler would fire up the burner when the water temp drops down to the 30's (burner will display just one bar on its scale) until it reaches mid 50's when the burner turns off. The water temp would run up into the 70's but would then steadily drop back down. This cycle will continue on and on. Each cycle takes about 4minutes. On the first night after the valve was replaced (Tuesday) the boiler temp did move into the 60's and 70's but by the morning it had dropped back down to the 30-50's again.

We've used up more gas than ever for an April and it's been so annoying. I had a local plumber who has knowledge of the system look at it today but I was at work so I couldn't press them on it and they hadn't seemed to achieve anything. They told my wife it might be a wiring issue but considering the wiring hasn't been touched, I find it unlikely but there could be some relays that have burnt out I suppose.

5 Wire Issue:  
I replaced the valve as instructed but I could only get a mid-position 3 port valve. It has orange, blue, green, white and grey. I thought since I don't need the valve in its middle position, I can get away with just wiring the orange to live, blue to neutral and green to earth. However, this now only open the valve to mid-position. As a temporary measure, I've manually opened the valve using it lever. I was thinking of simply connect the orange wire directly to the synchron motor in the head by splicing them or do I use one of the white or grey cables instead in order to get the valve to fully open when energised?

It's been a long one and I winged it all when typing this up so apologies for missing any details, typos or if bits don't make sense. Any help on getting the boiler running properly would be greatly appreciated. Otherwise I would have to call the company out and they'll charge loads because they'll have to travel across the country.

Thank you.

Boiler Not Constantly Supplying Hot Water to the Heating System - HW Cylinder Never Reaches Temp. H2 Panel.