central heating only comes on with h water, stumped engineer

[jackthom]

Bill I don't know how closely you've already looked at the pump but is it a variable speed one and if so is it set to max.

Failing that, assuming you have easy access to it and it's fitted with isolating valves, I'd be keen to remove and inspect it.

 

[MANDATE]

Billy! Can you confirm if you have a by-pass valve fitted. would be on a pipe leaving the flow pipe between pump and 3port valve. If you have, try opening it a little.
I'm thinking it may prove there is partial blockage if the 30sec increases on the basis that more of the water can flow back to boiler and increase the time before boiler cuts out.

 

[bonkersbill]

Under the fire is a knob with high and low marked, its set in the middle, i cant see any other switches or valves here, i will have to see how i get the fire out to look at the boiler more closley, i just cant see how the fire surround comes off to give me access to the fixing screws, when i do i will check the temp of out flow and see what else is there.

I cant see a bypass valve, there are 2 28mm pipes from the boiler to the HW tank and a 22mm from HW tank to Rads, various other pipes from HW tank to water tanks for water and vents. So if bypass needs another pipe to the boiler then there isnt one that i can see.

 

[gaswizzard]

Wrong post.

 

[bonkersbill]

i have had a look under the floor boards where the 22mm out flow from the actuator valve to the CH which goes to a T, from here 15mm to 1 rad, 22mm to the rest upstairs, from this 22m is another T with a 15mm which goes down towards the direction of boiler with a 15mm coming up from the direction of the boiler, if these are the out flow to the rads down stairs and return from the uptairs then i assume these are not big enough and would appear like the blokage discussed ealier, or there is another T which has another return but i cant see why this would take a different route to the boiler when all the others go strait down the side of the chimney to the boiler. The 2 main pipes from the boiler to the tank are in 28mm pipes so if there is no extra T can i assume if i change these 15mm pipes to 22mm that this will most likely solve my problem?

 

[snb]

from what you have said so far you are no nearer solving the problem.

Get a heating engineer out ( not a plumber unless they can do electrics) and tell them you think the heating wiring has been altered wrongly.

They will at least then re connect the wiring correctly so that the controls behave correctly

Then if the system still does not perform then it needs to be investigated for either wrongly piped or for a blockage

 

[bonkersbill]

Hi SNB, i dont know if you have read all my posts but i have never called out a plumber as the title of this post suggests, engineer stumped. Every one of the 4 heating engineers have found nothing wrong with the wireing, i have checked a wireing diagram and everything is where it should be and as far as i can tell the actuator is moving to all its correct positions when called to do so. I cant understand why you have made these suggestions when even i can see that a 28mm pipe to the tank reduced to 22m to the rads reduced to 15mm back to the boiler on the CH side cant be right, when HW is also on there is the 28mm return from the HW to ease the flow which is what alot of the comments on this post have been suggesting, either flow, blockage or Teed twice, so why have you re-suggested what we have pains takenly tried to ensure is not the problem?

 

[bonkersbill]

Are the 15mm pipes as described above to the boiler wrong and are they likely to be the cause of the boiler turning itself of after about 30 seconds? A few of you have been saying that this could be a blockage or narrowing of the pipes and i would like your oppinions before i start to rip out coduits and floor boards to get to them. Also are there flexible 22mm pipes that i can use as i will not be able to solder on the bend with out pulling out a new fitted wardrobe or smashing through an ornate ceiling.

 

[jackthom]

Bill, with only the CH on (for as long as it stays on) have you tried feeling the path of the heated water through the pipes you have now exposed.

I'd be keen to learn as much as possible about how hot it is, how far it gets and the precise path it takes. Do this as many times as it takes to get a better idea of how the system is connected and if some of that heated water eventually comes back towards the boiler, your questions about the return path may be answered.

 

[MANDATE]

There has got to be a explanation why CH is ok when on with HW but not alone, with the valve functioning ok
When CH is on with HW and the valve is in mid position it copes with the CH side even though there might be partial restriction. The reason being that water is also flowing through the HW side and preventing high temperature build up.
The difference when you have CH only is the HW is closed off so temperature increases and boiler stat operates.
The water flow depends on the' pump' forcing water around the pipe work which offers a 'resistance'.
The resistance may have increased some over time, but also the force of the pump will not be as effective. Also you don't have a by-pass valve.
It costs very little to remove pump or just the pump head and examine it. (and the valves either side of it)
I don't think you can assume it's ok because it works for HW. (my HW works fine and I don't have a pump for HW)
Secondly before ripping anything out, why not get some cleaner in the system with a view to reducing the resistance.

 

[bonkersbill]

i removed the actuator and turned on CH, the boiler stayed lit until i manually put the spindle in horizontal position (CH), just as a test i turned the spindle180 degrees to see if actuator was on upside down though every engineer says its not, boiler kept going, the CH pipe below actuater valve got very hot quickly but so did the HW return, but the CH pipe very very slowly (could be convection but not sure) started to warm up pipes only(I think this is coming from the HW tank because if i shut down CH these pipes stay warm, i switched CH back on, switched it back to CH position where boiler shut down, the grundfos pump always keeps going when boiler shuts down and this pumps cold water round the CH quickly, if i put it in mid posision this pumps hot water round CH quickly.

Recap valve positions appear to pump either hot or cold water round the CH quickly but not when its in CH position, but it wont pump HW round quickly when spindle is set to CH 180 degrees upside down position.

This makes me think the valve is duff though 3 engineers have sain it works fine???

 

[MANDATE]

Don't know if I've got this right! Bill
With actuator head off spindle, you set spindle 180 degrees from the CH position.
Then switch on CH only , actuator takes up the correct position and in doing so it lights boiler (via micro switch). and pump operates
Boiler does not close down after 30secs, so you have central heating as it should be normally.
Spindle is then turned 180 degrees (back to original position) and boiler closes down as per original fault.
If you can get CH only for a reasonable time period by turning spindle 180 degrees, that would prove a partial blockage is not the cause of boiler closing down.
Sounds as though the CH port is closed when it should be open, but I would not have thought the spindle and actuator could be misaligned.
Does the spindle not have a 'flat' machined at the end to prevent wrong assembly.

 

[MANDATE]

Based on your last message, I've been searching for a way in which the CH port could be closed when it should be open and I do believe and I may have found something.
The bottom of spindle will have a 'flat' so it blocks off CH leaving HW open, or blocks off HW leaving CH open or in mid position both CH and HW are partially open.
Now this is based on water entering the from the 'pump' port and going to left or right. lets say water goes from pump to valve and turns right for HW.

Now imagine if valve has been wrongly piped and water enters at the HW port and leaves at the pump port, it would perform correctly.
In mid position, none of the ports would be closed, so it would still perform.
Now in the CH position the HW port is closed so water cannot enter the valve at all. hence no output to CH and quick build up of temperature.
OK Based on this I think you need to establish if the flow from pump is going to the correct port. Could also explain why nothing could be found wrong with the valve functioning.

 

[bonkersbill]

I really thought we had cracked it with the water flowing the wrong way through the 3 way valve but it looks like its not. I ran off all the hot water as i was getting mixed results with pipes alternating between warm and cold. From cold HW on, the 28 mm pipe to valve port AB gets hot 1st, leaves through port B to half way up the tank, then out of bottom of tank to 28mm back to boiler. if i turn the valve to CH position i can hear the water rush through the valve port A and the CH pipe gets red hot but does not heat the pipe for more than about 8' before boiler shuts down. i then turn the valve to mid, boiler starts up and tank and rads start to get hot, this all suggests to me that there is flow through the all valve ports and all the pipe work but when valve is in CH position there is a pressure build up and the boiler shuts down. i've been studying a map i drew to the best of my knowledge of my system and can only guess at 2 possibilities, the 15mm pipes are too narrow for the 28mm out and return from the boiler, so pressure is building up, or could it be that the return from the CH is teed into the out flow from the boiler instead of the return, could this send water both ways round the rads until it builds up pressure from the water coming from the valve port A, this would mean there is no return to the boiler until the valve is set to mid position. i have no idea where the CH return is teed into the system.

 

[bonkersbill]

I would like some help on a few things, it was mentioned whether a knob on the boiler is set in the high position, it is set to mid, should this be on high? Does the boiler have its own pump or does the whole system just use the grundfos selectric? Should the 28mm pipes from and to the boiler be 22mm and should the returns from the CH be 22mm not 15mm?