Hi all,
I recently moved into a new (old) house a few months ago and moved/changed one of the radiators so I drained the system. At the same time I decided to change it from a gravity fed hot water system to a fully pumped S plan by moving the pump and motorised valves around (more on this later).
Details of current system are as follows:
- open vented
- 20 year+ old Glow-worm space saver boiler
- two Honeywell 2 port motorised valves (making it an S plan)
- 2 speed Grundfos pump (set to 2 at all times)
- combination of 22mm and 15mm copper pipe all round. 22mm is used to feed CH but where the T piece is after the pump the HW copper pipe is reduced to 15mm to feed into the HW tank.
I originally just moved the radiator and when testing my handywork I noticed that the HW motorised valve wasn't working (stuck open) so i decided to replace this (I never tested the system fully when I first moved in so I can't be sure of how the previous owners used to run the system - the HW motorised valve was set to manual so they must have known it was knackered). After testing the radiator I looked at the pipe layout and decided that it would be straightforward and more efficient to convert it to a fully pumped S plan from a gravity fed HW system. The main reason for this was that the pump was activating when calling for HW only anyway (which actually pumped water around the CH system as well?!) - and the CH motorised valve was actually placed first so you could only get HW if CH was switched on anyway. It was a very bizarre layout and made no sense when operating the controls. The wiring was for a fully pumped S plan system but the pipe layout was for gravity fed (and even that was a botch job).
Anyway I got around the changing all the radiators to TRVs (except for 2 which are lockshields left fully open at all times) and have now testing the system which is detailed below:
- CH only. Boiler fires, pump activates, CH motorised valve opens, CH works fine.
- CH + HW. Boiler fires, pump activates, CH and HW motorised valves open, CH works fine and have HW.
- HW only. Pump activates, HW motorised valve opens, boiler fires for about 30secs - 2mins then stops. Pump continues to run and HW motorised valve stays open.
Has anybody got any idea as to what could be causing this? It can't be the thermostat on the HW tank as the pump and motorised valve are still both running/open and it works fine when using CH + HW. There is still a little bit or air in the system but it is working it's way out (by bleeding the radiators). No inhibitor has been used yet until I know I won't have to drain the system again. There can't be a blockage or air trap in the HW circuit as I get HW when both CH + HW are switched on. Everything seems fine until the boiler cuts out.
It's driving me crazy!
Many thanks in advance,
Paul.No hot water, heating fine.?Check if you have one radiator (usually the bathroom) getting warm when hot water only is on, some system are piped with a loop through a rad from the hot water, if this is the case, the water is taking the easiest route to the rad. It is a water resistance problem somewhere in any event, this is just one suggestion. You may have inadvertently linked flow to flow on hot water, this will let the water flow to a degree but will shut the boiler down quickly when the pressure backs up and the boiler overheats, if the hot water is not returning but is getting to the cylinder, it is one of the above.No hot water, heating fine.?Is there a problem in the controller, affecting the signal to the boiler when HW alone is selected? Can you check the electrical signal from the controller in all situations?No hot water, heating fine.?Hi - %26quot; HW only. Pump activates, HW motorised valve opens, boiler fires for about 30secs - 2mins then stops. Pump continues to run and HW motorised valve stays open%26quot;
For what it's worth! The boiler WILL only run for short periods when supplying hot water only. This is because it only needs to heat the (relatively) small amount of water in the primary circuit. Are the flow and return pipes, to the coil in the cylinder, about the same temperature? The boiler will not cut in again until the temperature of the primary circuit drops.
Are you SURE that the pump continues to run when the boiler shuts down? SOUNDS like a wiring issue. You could mail me a pipework diagram/photos of the installation if you want.No hot water, heating fine.?just by reading and not seeing the layout i can only deduce that somehow the primary return is not a return but instead has been teeed into the flow circut of the ch.The hot water you are getting when you have your ch +hw on is only because the primary circut is returning thru a radiator. to test this set your pro gamer to ch/hw on and close off all radiators manually.if primary flow goes cold its return is secondary ie. tru a radiator. This is a very inefficient way of heating water.
easy fix if you can access the pipe work .good luck with it.
