No hot water, heating fine.

[kp7722]

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.

 

[gas_man_gaz]

ya say it was a gravity hot water pumped heating system originally then ya go on to say the hot water valve was left manually open so they new it was faulty? doesn't make sense, any chance of some picture of the cylinder and pipework including the valves and pump?

 

[gas4you]

- 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.

Am I missing something here Sounds quite normal operation especially if the boiler stat is turned quite low

 

[kp7722]

Hiya guys,

Thanks for your reply. I sketched a couple of pictures to show the before and after shots. I can forward them to you if I can have your email addy?

Right I'm back at home now and have tested it further. Have tested all thermostats and all are working. All are set high for testing.

When calling for HW + CH:
CH valve opens. HW valve opens. Pump runs. Boiler fires. All is hot until room thermostat temperature is reached. Water is not at max temp but boiler turns off.

When calling for CH only:
CH valve opens. HW valve remains closed. Pump runs. Boiler fires. All turn off when room thermostat temperature is reached.

When calling for HW only:
HW valve opens. CH valve remains closed. Pump runs. Boiler sometimes fires and when it does, only for a couple of minutes at the most. Water in return pipe is only just warm. Now here comes the strange part. If I set CH valve to manual (open - Honeywell so microswitch remains open and therefore doesn't instruct boiler to fire) the boiler fires within 30 seconds. It's almost as if the pressure is too great going into the HW cylinder therefore the boiler cuts off. Opening the CH valve manually seems to relieve the pressure. The HW light on the controller stays lit throughout.

Any ideas???

Paul.

 

[gas4you]

Sounds like a blockage in the cylinder coil, or the pipe work in the flow leading to it.

How much pipe work did you replace when changing to fully pumped.

 

[gas_man_gaz]

can ya post the pics on this site? if ya had a gravity hot water pumped heating system to begin with you wouldnt of had a hot water valve! mite be a prob with the way ya piped it up

 

[kp7722]

Not sure how to post piccies on here. I knew facebook would come in handy one day!

http://www.facebook.com/album.php?aid=9027&l=bc8ac&id=544791297

In this album you can see both my old system and new system. I'm pretty sure the HW valve was set to manual on the old system - it was knackered. I haven't messed with the wiring so the actual controls operated on the old system like they do on my new (and not improved!). I can also remember vaguely that we could only get HW if the CH was on as well.

Cheers guys,
Paul.

 

[gas4you]

Wheres the vent and cold feed in your diagrams

 

[kp7722]

The cold feed for the HW tank itself (i.e. domestic and not through the coil) is at the bottom of the HW tank (22mm). I presume this leaves through the 22mm in the centre, on top. The feed from the expansion tank (which also serves as the vent/overflow?) runs down the side of the HW tank and tees off at the top to 15mm and into the HW tank's coil. This 22mm then carries onto the boiler. 15mm pipe also comes out of the HW tank with the HW valve on (as shown in the diagram).

Does this make sense? Am i right in thinking that I have actually got the flow wrong and that the original system may have been fully pumped? Have I got the labels for the flow wrong? Could the water from the boiler come up the 22mm to the 15mm tee at the top of the HW tank, then leave out of the top to the HW valve and then down to the rest?! I've been trying to work it out all evening! If this is the case then that obviously means that we get (or should I say would have got) HW only, HW and CH? The water from the boiler always goes through the HW tank and gets pumped back to the boiler? If that's the case then how does the water get to the radiators and back to the boiler?

Cheers,
Paul

 

[gas_man_gaz]

from the diagram ya had a s-plan before with the flow and the return the wrong way round! have ya got any actual photos so we can see the job lot (cylinder, cold feed, open vent, valves) can get a better idea of how its piped n weather its right that way

 

[kp7722]

gas_man_gaz you have just confirmed what I have been thinking all night! I feel like a frickin' idiot to say the least!

One more question though. How does the feed go to all the radiators and then back to the boiler? If HW only the water passes through the coil to the HW valve down to the pump and back to the boiler (what's the bypass there for?). So how does it go to the rads? The CH motorised valve pointed up...

 

[kp7722]

Chaps, if you would be so kind to check my album again. Am I correct now? That is what the original system looked like.

But as I said before - how does the water get to the radiators?

 

[kp7722]

It's obvious now. The water from the boiler will be teed off to both the HW tank and the CH valve, won't it? Therefore you can have them totally independent of each other as well as together. That's why all the controls and stuff operates the way they do.

Am I right?

 

[gas_man_gaz]

the bypass is there to get rid of any heat, and basically so ya pump cant pump to a dead end. what should happen is the boiler should heat the water, the pump sends the water from the flow out of the boiler to the two valves (with a small amount goin down the bypass). dependant on which valve is calling, eg heating the valve will open and direct it through the radiators and to the return which leads back to the boiler at the opposite side.

any chance of some photo's?

 

[gas_man_gaz]

more and more diagrams are popin up!