My F&E tank ...(image omitted) ... seems to have separate expansion pipe
The pipe you marked as expansion is actually the vent pipe. Where is the other end? I can't see anything in the other pics
Valve E is a bypass valve. Shut this completely then open one turn.
Valve D controls the flow through the HW cylinder. You could try closing it down, as if it was a lockshield valve, so the HW cylinder does not get more than its fair share of the circulating water.
thanks I'll try that.
I don't expect you have the installation manual for the boiler (it's very old in any case) but, if by chance you do, there should be instructions for setting the bypass (Valve E). The important thing is that the boiler will require a minimum flow rate and this is determined by how open Valve E is. One turn from fully closed is normally about right.
I'm not sure have I got the message right...
If the programmer is in CH&HW position and room tstat calls for heat then boiler fires up and HW is heated because there is no MW to cut it off. When room tstat reaches desired temperature it should stop boiler and pump until room temp drops and tstat starts calling for heat again in the meantime boiler should keep quiet.
Correct. That is what your system should do
Here is how it's working in my case:
Programmer in CH&HW position, room stat turned down to min. MW is closed but pump is working and boiler fires up anyway. Should I assume that installation is not wired properly?
This means that the HW temperature is controlled by the boiler temp, which is OK in the summer but not very economical in the winter when the boiler temp will need to be higher. I think the previous owners who had the system installed did not want to go to the expense of installing a second MV so they put in valve D instead, which could be partially closed in the winter to prevent the HW getting to hot.
The wiring is not wrong as it is the only way of wiring the system so you can have HW without CH.
I've looked on wiring diagrams posted by you but I couldn't find anything that looks like my installation they all are using cylinder tstat and I think that C Plan is the closest.
C plan is for systems which have the pump only in the CH circuit and not the HW, which relies on gravity (hot water rises, cold falls) for circulation.
What you have is an S plan without the second MV and HW cylinder thermostat. This will explain it all:
Honeywell S-Plan
Alternative solution
Just checked the Danfoss web-site for details about your time switch. They show a wiring for your system which just uses a cylinder thermostat and not a second MV. The only disadvantage is that you cannot have CH only switched on. But it will turn off the boiler when the HW cylinder is up to temp. This is the cheapest solution as it only required a cylinder stat, which cost about £15, and there is no plumbing involved.
Now this system is fine in the summer as the Cylinder stat will turn the boiler off when the HW reaches temp, say 60°C
but it will only partly work in the winter as there is no way of preventing circulation through the HW cylinder while the CH is running. For this, you
must have a second valve.
Details are here:
Danfoss 102 Instructions
It's wiring diagram 2 which you need.
I am sure that, with all the expense of a young baby, you will be trying to keep your expenditure to a minimum but, while you are embarking on this update, have you thought about updating your room thermostat. If it is like the rest of the system it is probably an old mechanical type.
There are two routes. The cheapest is to replace it with a digital ones such as the Honeywell DT200 are more accurate and will keep the room at a more constant temperature this will cost about £20.
The alternative is to replace it with a programmable thermostat (combined timer and thermostat) such as the Honeywell CM900 range. This allows you to set different temperatures at different times of the day and even for different days if required. They range in price from £45 (wired) to £90 (wireless)
OFF TOPIC
I'm kinda angry because before we bought this house I was bit concern with CH installation especially boiler so I've paid "reputable" company to do the check-up and find out about it's condition they have said that everything is OK and it just needs to be power flushed. They took 60 pounds and when we moved in after 2 weeks I found two leaking radiator valves and now I've got all this problems with CH.
I don't understand it because if they have said that installation needs updating then I would have good reason to ask for house price reduction and I could use saved money to install new system and probably I would ask them to do it so they would earn more money.
At least you did the right thing by getting a survey done; not many do that. It's unfortunate that you chose the wrong firm. Were they recommended by the seller's estate agent by any chance, or was it one you already knew?
Presumably they commented on the age of the boiler and the lack of proper controls and that it did not meet current building regulations.
So how did they know it needed to be powerflushed? You can't tell that just by looking at the system.
You will, eventually, have to replace the boiler but you will be pleased to learn that, if you do decide to add the second MV and cylinder stat etc, the expense of doing so will not be wasted.
