Can't run CH and HW at same time

[iandvedwards]

Hi,

We've just purchased a new house and have discovered that when the CH and HW are both on, only the hot water cylinder heats up and the CH remains stone cold. Both work ok on their own. In addition the CH is a bit slow and rads take a while to warm up, I've noticed the boiler comes on for about 3-4 mins then goes off again. The room thermostat is clicked on but the boiler cuts out. This means it pretty much never reaches the thermostat temp setting.

A friend of the family had suggested the grundfos pump may be the cause of the 2nd issue, however we are not too sure about the 1st issue, any thoughts?

We have a potterton kingfisher II boiler and hot water tank with horstmann 425 diadem programmer.

Thanks!
Ian

 

[dcawkwell]

Yes sounds like the pump isn't turning.
Remove the centre screw from the pump and stick a screwdrive in the hole. If the pump is spinning you feel the shaft hitting the screwdriver.

 

[iandvedwards]

Removed the centre screw and the the pump was spinning. Screwdriver was in but made a noise when hitting the shaft spinning. Any thoughts?

Also any thoughts on not being able to run CH and HW at the same time?

 

[dcawkwell]

Removed the centre screw and the the pump was spinning. Screwdriver was in but made a noise when hitting the shaft spinning. Any thoughts?

Also any thoughts on not being able to run CH and HW at the same time?

Pump is probably fine as central heating wouldn't work without it.
So sounds like there must be a 3 port valve maybe wired wrong.

 

[iandvedwards]

Or a faulty programmer? [/quote]

 

[Whitespirit66]

Also any thoughts on not being able to run CH and HW at the same time?

Perhaps you have a W Plan system, where the motorised valve prioritises hw. You could change the valve to a mid position valve instead to make it a Y Plan. You can then have hw, ch or both together.

 

[HERTS P&D]

Might need a balancing valve on the hot water circuit.

Andy

 

[picasso]

Might be better with a crystal ball for all the information we got

 

[JohnD]

50p on balancing.

 

[HERTS P&D]

Call out BG and they will quote you £800 for a power flush and while they are there they will fit a balancing valve free of charge.

Andy

 

[dcawkwell]

Tank thermostat has probably gone.

 

[stem]

The boiler sounds OK. It seems that it is heating the water up to the temperature set on the boiler thermostat and then switches off because the hot water it has produced is not being transferred to heat emitting devices (radiators / hot water cylinder) efficiently enough. (If the boiler continued to run it would actually boil the water)

So the problem appears to be the distribution of the hot water produced by the boiler around the system. There seems to be some circulation for either the hot water or the central heating but not enough for both, so I would suggest.

1. Pump not working properly or speed setting too low.

2. Manual by-pass valve (if fitted) open too much & effectively creating a short circuit across the pump and boiler where most of the water flows, so not enough flow left for rads and hot water system.

3. Balancing as already mentioned, water will take the easiest route and loves a short cut.

4. Partial blockage restricting the flow of water in the pipe system.

I can't comment on motorised valves as you don't say you have them or not and if you do what type they are.

 

[Agile]

Ian, you have lots of suggestions as to all the possibilities.

Its now down to you to learn enough about all of them to decide which is the problem(s) in your case.

Or to get it sorted out quickly call a competent engineer to diagnose the problem. Many like me are quite happy to just diagnose the problem and leave you to fix it.

Tony Glazier