central heating only comes on with h water, stumped engineer

[doitall]

Just to make it quite clear zero flow through the heating, will not cause the back boiler to sing and dance or overheat, it will however shut down quite happily with the boiler stat.

If the boiler is making funny noises it suggests trapped air or scale.

 

[bonkersbill]

Opened all rads, HW & CH on at programmer, turned 3pv manually to CH and boiler shut of.
i dont have access panel to side of boiler but i will make one this afternoon, where would be the best place to find the pipes going into the boiler, level with top of fire, middle or bottom.
If TRVs are thermostats on rads then i have 3 out of 4 on downstairs rads, i have turned the heating up full to see which are getting hot, all but the 2 largest rads in the front room are getting very hot, i think these 2 may be the last in the circuit, though you say you are not concerned and that they may just need balancing, is it easy to balance them so we can rule this out?
I will rerun the test of turning up the boiler to see what happens as i have had trapped air in the past, since i flushed the system and refilled leaving my top rad air release open, the system seams to have filled properly without any air.

 

[stardanny]

i dont have access panel to side of boiler but i will make one this afternoon, where would be the best place to find the pipes going into the boiler, level with top of fire, middle or bottom.

Middle level of fire.

 

[doitall]

No I'm not concerned to any extent, if you want to balance them, then open or close the lockshield valve till they all get get the same temperature.

What does concern me is, "All the rads are getting very hot except the two in the lounge" That indicates something is shutting the flow OFF.

Is there an MV you don't know about in the duct perhaps.

Do you know whether the TRV's have been added during the alteration.

You didn't answer how accurate you think the drawing is.

At a quick glance it has all the hallmarks of a one pipe system.

 

[UpgradeME]

What does concern me is, "All the rads are getting very hot except the two in the lounge" That indicates something is shutting the flow OFF.

Is there an MV you don't know about in the duct perhaps.

OP, can you try turning off all the other radiators appart from the two in the lounge. Then with the 3PV in the CH&HW position, check to see if they now heat up? (make sure both ends of the lounge radiators are fully open)

If they heat up, you have proved you have a two-pipe system & balancing may resolve that issue at a later stage (I wouldn't worry about balancing at the moment).

If they don't heat up, it is likely that there is a flow restriction on the pipework leading to/from those radiators. I would be tempted to remove one/both of them (isolate each side before removing and be careful of possible sludge dripping on carpets), take radiator(s) in the garden and flush out with a garden hose. With one of the radiators removed, I would then attach a hose pipe to the valves/pipework and drain some water looking for any debris in the system.

 

[Mikefromlondon]

Opened all rads, HW & CH on at programmer, turned 3pv manually to CH and boiler shut of.
i dont have access panel to side of boiler but i will make one this afternoon, where would be the best place to find the pipes going into the boiler, level with top of fire, middle or bottom.
If TRVs are thermostats on rads then i have 3 out of 4 on downstairs rads, i have turned the heating up full to see which are getting hot, all but the 2 largest rads in the front room are getting very hot, i think these 2 may be the last in the circuit, though you say you are not concerned and that they may just need balancing, is it easy to balance them so we can rule this out?
I will rerun the test of turning up the boiler to see what happens as i have had trapped air in the past, since i flushed the system and refilled leaving my top rad air release open, the system seams to have filled properly without any air.

The two which are not getting heated up as others, couldbe due to rads have valves on both sides, so ones used for balancing are the ones which have a free spinning knob, or just a cover, it does not engage with the spindle so it will not turn the spindle, but you can remove this cover and use a knob from the other side of the radiator and make sure that both sides are fully open, this should allow all the CH flow to move through just for now to rule out any other problems, you could balance them later on, using guides from these forums, or even google for that.

but for now each rad has two valves both must be fully open to rule out flow problems. good luck in your tackling this problem.

just in case there is any confusion, valves are open when turned anti-clockwise, TRVs open when you turn up the temeprature setting to highest.

 

[bonkersbill]

i've now had all the rads on full for at least an hour with my hand on one in the front room, this has eventually built up to about same temp as the rest though slowly, the other is still warm to hot with no air in. the temp has been fluctuating up and down all the time, i presume because the HW is being satisfied. i have now turned all the rads off except front room and will leave thermo on full for a while to see what happens.
i could not tell you if there is another MV hidden some where, the drawing in the circle i drew was as accurate as i can do other than they are not in exactly the correct places, the rest is guess work, i will open up the side of the boiler to find out whats happening hear, could do with knowing the best position to open it up though, will have to do this another day now

 

[doitall]

about 3ft ish.

I would look under the floor on that side first, there maybe a trap so should be easy once the carpets rolled back a little way

 

[bonkersbill]

Both rads in from room are now red hot, hotter than any of the others were. Just to confirm, valves were open all open prior to these tests except the one rad in front room which i only have open slightly as its under the window and plasma tv, cant have heat sorce under plasmas, i am moving this in next couple of weeks and removing the other rad in front room.

 

[doitall]

So all the rads are getting red hot by playing with them, is the htg and hws calling or just the heating. what position is the MV in.

 

[UpgradeME]

Both rads in from room are now red hot, hotter than any of the others were

In which case you appear to have a good flow through them and have a two pipe system (flow & return). With the system as it is, can you try turning the 3PV to CH only and see if the boiler still cuts out?

 

[bonkersbill]

still got only front room rads open, HW & CH on at programer, Manual valve in mid pos, HW is calling and rads are hot, tried turning valve to CH pos, boiler shuts off.

 

[bonkersbill]

just done a retest of turning up the heat on the boiler, it only starts banging and you can hear the water bubling and boiling almost straight away when it is turned to CH only pos at 3pv, it sounds ok on all other settings

 

[doitall]

How are you changing the MV, manually or with the stat/timer

When the boiler is banging and crashing is water being pushed over the vent pipe into the header tank.

 

[bonkersbill]

Manually at the 3pv spindle, the actuater is off and doing its thing moving to different possitions as and when.
i will have to check the header tank.