central heating only comes on with h water, stumped engineer

[matt1e]

Almost certainly a wiring fault, if Bill preferably posts the pics to me we can get it up and running in no time

I disagree, reading through I'd say it was definatly a circulation problem on the Rad circuit, the op needs to sort out his pipework

Matt

Matt,

If it was a circulation problem, why does it work when the DHW is on.

because there is still "some" circulation in the rad circuit and the boiler works fine while its getting a good return from the cylinder
as soon as the HW circulation is blocked off via the 3 port there is not enough flow in the rad circuit to stop the boiler thermostat switching the boiler off (or the boiler "kettling" when the stat is up high)

Matt

 

[plumbplumb]

Really better advised using a multimeter to fault find on heating wiring.....

Only had it once but worth noting..

Valve worked as it should then by turning HW and CH on and off to simulated different situations valve started acting up but only in certain positions.

last hope was tested wire to cylinder stat and had continuity through all three. Small nick in wiring to cylinder stat kept throwing valve into spasms.

 

[doitall]

Do you want to read what you just wrote first Matt.

Couple of clues so we'll use the word should be.

The return is common, it makes no difference whether one or the other or both is on.

It works when hot water and heating is on, so when the cylinder is satisfied, the valve will travel to heating only and actually increase the flow to the rads.

 

[matt1e]

Do you want to read what you just wrote first Matt.

Couple of clues so we'll use the word should be.

The return is common, it makes no difference whether one or the other or both is on.

only common pipework, it still has differing flowrates through different parts of it (circuits)

It works when hot water and heating is on, so when the cylinder is satisfied, the valve will travel to heating only and actually increase the flow to the rads.

It doesn't work when water and heating are on
when the valve closes off the hot water port the flowrate through the boiler drops the boiler heats up and and so the stat switches it off
the rads may heat up while the hot water is also calling but,
as a cental heating system.......It doesn't work!

Matt

 

[doitall]

It does work when htg and hws is on, or have I missed something.

It's only common when the htg return joins the primary return.

All the heating returns should be connected prior to that, and as such are not affected by what the HWS does.

Most likely problem is the MV not moving to HTG only or the boiler pump not switching.

Of course there's other options, but one should be able to ID the problem within a few hours easy.

 

[doitall]

Hi, my Y plan ch will only come on warm to hot when hw is on, i had engineer out who said everything was working but was scratching his head as to where the return pipe was to the boiler and said he could do no more. i had danfoss hsa 3 which got very warm whether connected to the valve or not so i replaced it, , still the same, i replaced ch thermostat and programmer, no change, after months of messing i realised i had removed a rad and had joined the in pipe to the out, I've now put in a valve in the off position and thought this must be the problem, now i get very hot rads when hw is on with ch on but the boiler will only come on for 30 seconds when ch comes on on its own, any ideas as this has been a pain for nearly 2 years and no-one seams to know what to do.

This is the original post and typical of an electrical fault.

I would almost say the pump is wired wrong but really need to pics.

 

[matt1e]

Hi, my Y plan ch will only come on warm to hot when hw is on, i had engineer out who said everything was working but was scratching his head as to where the return pipe was to the boiler and said he could do no more. i had danfoss hsa 3 which got very warm whether connected to the valve or not so i replaced it, , still the same, i replaced ch thermostat and programmer, no change, after months of messing i realised i had removed a rad and had joined the in pipe to the out, I've now put in a valve in the off position and thought this must be the problem, now i get very hot rads when hw is on with ch on but the boiler will only come on for 30 seconds when ch comes on on its own, any ideas as this has been a pain for nearly 2 years and no-one seams to know what to do.

This is the original post and typical of an electrical fault.

I would almost say the pump is wired wrong but really need to pics.

well you should read the rest of the posts

since that post
the electrics have been checked
valve operation has been checked
valves been replaced
valve body has been manually operated
pump has been checked that it is operating while on heating
boiler has been checked that it has a demand while on heating demand
it looks as though the return for the cyl is 28mm as is the flow
it looks as though the return for the rad circuit could in 15mm and the flow for the rads in 28mm down to 22mm

system wise
the boiler works as expected as long as the cylinder with its 28mm flow and return are connected hydraulically

if the boiler is connected hydraulically to the rad circuit then the system doesn't work, the boiler shows signs of poor flow rate (kettling, getting to stat cut off set-point too quickly etc)

so we have a boiler connected to two circuits via a common pump
boiler works fine if both circuits are open
boiler works fine if one circuit is open
but not the other as this one one its own cause's the boiler to cut out too quickly or kettle then cut out if the stats turned up to compensate

why do you think the boiler is behaving this way connected to one circuit and not the other?
add in the fact that the system looks as though it could be an old gravity hot water open vented system converted (not very well by the looks of it ) to fully pumped and one circuit looks like its plumbed in 28mm while the other is in 22mm reducing to 15

what do you think might wrong with the boiler,(well system really) judging by the above description of the fault ?


Matt

 

[doitall]

I haven't read any of the previous posts, maybe skimmed a few but thats all.

Most of the time I prefer to form my own opinion.

You mention pics are there some about.

 

[matt1e]

I haven't read any of the previous posts, maybe skimmed a few but thats all.

Most of the time I prefer to form my own opinion.

You mention pics are there some about.

as us all! fair dos
I don't think he's posted any yet mate
it would be a help though

Matt

 

[4xpaws]

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.

Bonkersbill, to confirm, one of these two 28mm pipes from the boiler has a couple of pipes tee'd off it (22mm vent and 15mm cold feed both running up to a cistern in the loft ). Next along fitted on the 28mm is the pump, then finally the 28mm goes into the AB port on the 'base' of the 3 port valve. The arrow mark on the side of the pump housing should show its pumping towards the 3PV.

From the 'B' port on the 3PV, 28mm goes to the upper connection on the HW cylinder.

On the lower connection on the HW cylinder the 28mm returns back to the boiler. There's no other visible tees on this 'returning' 28mm. However, some of the 28mm is hidden in a conduit running to the boiler

The "22mm from HW tank to Rads" pipework you mention, is this the 22mm from the 'A' port on the 3PV feeding the CH circuit?

the 2 15mm pipes from upstairs rads go down the same conduit as 28mm pipes to the down stairs rads,

I assume the cylinder's upstairs, and the 2 15mm pipes are definitely from rads rather than HW & CW supplies for eg. a cloakroom.

I'd be tempted to cut a hole/ remove the face of the conduit to see what tees are hidden on the 28mm running within it.

It doesn't read like a wiring problem as removing the actuator head when the programmer and HW stat are just calling for heat, then manually turning the valve spindle to CH only position causes the boiler stat to kick in as the heats not leaving the boiler.

i can remember the rads would get warm in the summer when CH was never on

It reads like reverse circulation. Installer's tee'd in cylinder return in the wrong place when converting the system from semigravity to fully pumped and either the CH flow coming off the 3PV is a dead leg, isolated or blocked prior to the first tee on it feeding rads that heat up when the HW is on.

 

[geoff@cetltd]

Hi and thanks for all the details,

i have had another engineer out, 3rd one and again he cannot find out what is wrong, he says everything appears to be working but the boileris either not coming on when ask by CH or it comes on then turns off after about 30 seconds, im not paying for another so it looks like im going to have to do it my self.

You should never have paid anyone who was unable to diagnose your problem!

If they dont have the requiired skills they should not have agreed to come to you!

All you need is just ONE competent heating engineer!

Tony

a bit like looking for a virgin in australia, eh Tony?

 

[stardanny]

About these 28mm pipes, did it used to be gravity primary with pumped heating that been changed to fully pumped?

Is the radiators return pipe goes straight to boiler or via 28mm return?

These back boiler use injector tee fitted on gravity return with heating return tee in to help with gravity moving when heating is on.

Maybe the injector is nearly blocked?

Just a thought....

Have you check these yet? Can you take a pic of where the pipes going into side of chimney breast? A pics paint a thousand words.

Dan.

 

[bonkersbill]

 

[bonkersbill]

 

[Agile]

Clearly those 'knots' in the cables create an inductance and prevents the circuits operating correctly as a result of the increased impedance!