Hi, when I purchased my home 20 years ago from new I asked for a four pipe system to fitted. I have an oil fired warmflow boiler with a Danfoss control unit. I can have separate hot water, by pressing the hot water on the control unit and to get heating I press both the hot water and heating buttons together and get both the hot water and heating working together. It is only now after being advised my Control until should be able to have have heating only. When I press heating only on the unit, the Led lights up but the boiler doesn't fire-up. Can anyone advise what the problem may be.
I can not see any motorised valves, heating systems normally follow plans, S, Y, W, C etc. all but the C plan normally have motorised valves, the C plan comes in different flavours.
Back some years the programmers had two options, 10 or 16 programs and there were switches and mechanical locks to switch between the two, with no tank thermostat and no motorised valves using thermo syphon (gravity) for DHW there were only 10 options, it was counting off as an option so not really 10, you could have it one once or twice a day, either DHW only or DHW and central heating. There was no control for DHW so in summer you had to select how long it ran for, so boiler would some times fire up and only heat pipes as tank already hot.
So next was a thermostat was added to the DHW tank, this made no difference in winter, however in summer the boiler could be left on 24/7 in DHW mode and it would only run when the tank had cooled.
Next mod was to add a motorised valve to the DHW, if the boiler was suitable and this would limit the temperature of the DHW in winter, because adding the valve means the boiler can't cool by heating the DHW some boilers (mine for example) it is not recommended to fit the motorised valve.
With the motorised valve fitted, you can use the full 16 options and have CH without DHW.
With some C Plans the CH would thermo-syphon mine had that problem, so some times it uses thermostatic radiator valves to stop flow in summer, some times a motorised valve is fitted, because mine has two zones, and two pumps, it was found using either zone on its own would cause the hot water to travel backwards through the other zone, so two motorised valves were fitted to central heating, to stop reverse flow, and thermo-syphon in the summer, but I can't turn off DHW or the bathroom towel rail, they need to be always on to let boiler cool.
I will guess you can't turn off DHW, and leave CH on? you could move the slider and dip switch in the programmer to allow you to set it so only CH but it would still heat DHW anyway unless you have a motorised valve and tank thermostat.
Thanks for a very comprehensive reply. From my limited knowledge I must have at least one motorised valve. Using my logic, when I press the hot water button on my control unit, only the hot water boiler heats. When I press the Central heating boiler, the heat comes on. How does the central heating pump get the power to switch on, because if I press this button only, it doesn't power up, only when I press the two together.
I have a hot water tank thermostat which is set at 75, I read it should be set at 60. If the hot water in the tank reaches say 75, does this signal to the control unit to switch off. If this is the case my heating would switch off, which I don't want to especially in the winter.
Where would be the normal place to fit valves, I know there are none at the boiler in the garage.
Valves if fitted normally either at boiler or at the cistern. [attachment=1]C-Plan.jpg[/attachment] Above is the full C Plan, and below is very basic C Plan.[attachment=0]C-Plan_old2.jpg[/attachment] There is also one half way between the two, it was the most common method, and the early version was often used to pre-heat home in morning and evening before the fires were lit, it was never really used as only way to heat house. However with modern programmers the old system can be made to work quite well, I have a Nest wall thermostat and 9 electronic TRV valves and it does a reasonable job. But in summer there is a problem, how long to run the boiler to get the water warm enough? The idea is water should be over 55°C to stop legionnaires at least once a week, but I have no thermostat, and the boiler starts to cycle after 20 minutes, the cylinder just can't absorb the heat quick enough, what I want to do is add a timer for the immersion heater which is thermostatic controlled so after boiler has run, the immersion heater can run and ensure at least once a week the water is hot enough.
In winter it really does not matter, I turn hot water off, but it can't actually go off, it is heated every time central heating runs.
Hi, Eric, once again thanks for your help and the drawings. I don't think mine is wired / plumbed like that. I'll try and explain the way I think it is has been installed. At my boiler I have two pumps, the black one feeds the central heating the green one the domestic hot water ( see attached photos). I have checked the electrical wiring at the boiler. When I press the DHW, the boiler fires and the green pumps starts and heats the hot water, with 2 pipes one going in to the pump from the house, going in to the top of the boiler and coming out of the boiler and going back in to the house. When I press the Heating only, a signal is sent from the control / programmer unit and the pump runs ( black pump in picture), only the boiler doesn't fire. Once again there is a pipe from the house going in to the top of the tank via the pump and coming out the bottom and going back in the house. With my limited knowledge of plumbing, could it be as simple as a strap missing( white electric switch) where the electrical feed comes from the Programmer that when the pump gets a signal to switch on and run, this strap extends this signal to start the boiler.
Also could you advise what speed you set the pumps at. The Domestic Hot water is set a 2 and the Heating is set at three. I have read somewhere, that if the heating pump is set too high it can cause air in the radiators. I have one radiator which I have to bleed continually and it has been like this for nearly 20 years.
Hi Eric, thanks, I really appreciate your help and advice, with regards to backflow, does this mean if I was using the boiler for Central Heating only an element of the heat could be transferred to the Domestic Hot water. I know when I have the DHW running only, the radiators both upstairs and downstairs remain cold.
Without working out exactly how plumbed and wired can't answer, using non return valves can stop back flow so one system does not power the other, but I had to carefully draw out my system to understand what it does, the basic idea with most systems is.
The programmer sends a feed to hot water and/or central heating thermostats, and the thermostats feed the motorised valves, and the motorised valves feed the boiler, the motorised valve acts as a relay.
By using the normal closed contacts in the hot water thermostat it is possible to have a single motorised valve.
Also if you never turn the domestic hot water off in the winter you can do away with the motorised valve and control if central heating or not by switching pump on/off.
But the domestic hot water has always been thermo syphon when no motorised valves have been used.
Thinking about it I suppose you could have one pump always working when boiler switches on for domestic hot water, and second pump for central heating, but never seen it done that way.
To progress I would need to work out both how plumbed and how wired, and I can't really do that with messages on a forum. You need some one physically there on site to work out what you have.
[attachment=0]C-Plan_twin_pump.jpg[/attachment]I have thought about twin pumps, and this would work, however if you look the pump and relay in the red dotted lines is doing the same job as a motorised valve, so really don't see why it would be done?
In days gone by I had some great ideas on how to solve a problem, however as I got older and wiser I realised at some point some one other than me may need to repair it, so either detailed plans are required, or use a standard system.
I have drawn up a careful plan of my system, so in the future when I am not able to repair myself some one can do it for me, drawing up the plans was good, as I realised I had missed a bit, and needed a second relay.
But in your case to try and work out what you have is not easy, I see some steel wired armoured cable (SWA) going into a box at the side of the boiler, and that box could have a relay inside, and in real terms it could be hidden anywhere.
I was shocked when the guy came to service my oil boiler, I simply don't have the tools to set the pressures to ensure burning correctly, but while chatting to him, he said how he fitted a motorised valve without plumbing it in to use as a relay. It seemed daft, however most relays don't come in a housing, so although the relay is cheap enough, by time you have bought an enclosure, glands, and cable likely it would cost same as a valve, so not sure what would be best?
It cost me nothing, I had the relays, the bases, the glands and the box in my garage, it was just a case of fitting. But they are old, using a valve base, and although in theory if they go wrong, all that needs doing is unplug one and plug in another, likely when I go to local supplier I will find no stock.
You want some thing which others will understand and also kept on the shelf in local supplier. Having no heating for a few weeks waiting for bits off internet is no fun, every thing needs to be local, and if it goes wrong you want to be able to ring local firm to fix it.
Great fun for me trying to work out how to do it, if it goes wrong I am not cold, so think time to get some one in, if there is a sticker saying who installed it, likely they are best people to repair or modify it.
Hi Eric, again thanks and apologies for my delay in responding, I took myself off on a short break. Its a pity I took 20 years to try and resolve this, if it had of been in the first 10, I could have got the house builder back. I may be able to find the original plumber who installed the system, but if not I will have to call in someone to fix and possibly add a relay somewhere in the system. I know its now at the boiler or at the expansion tank, only other place is under the floor boards, and I don't want to have to lift them to try and find a relay which may not even be there. Once again thanks.
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