Heavy condensation in loft

[dkbb]

I have an open vented 'y' plan heating system, an indirect cylinder and a Potterton Flamingo (40K btu I think..) CI wall mounted boiler in a small 3 bed semi. Boiler in garage with balance flue through wall.
F&E tank and HW cold feed tank in loft.
All the rads have trvs fitted except the one in the hall, where the room stat is located.
The cylinder has been replaced and nearly all the pipe work replaced with an air seperator added to try and alleviate air build up in the hall rad.
I am reasonably competent with CH but not an expert...

In general the system works OK all new controls seem to turn the CH/HW on and off correctly, shutting the boiler/pump on and off as normal.

The problem I have, occured before the new pipework/cylinder was installed and has occured once since the new pipework installation.

It appears that the primary water is getting so hot that it is heating the water in the F&E tank to the point where it is evaporating into the loft space.
The boiler main stat (big dial on front) is set at 2 of 5
The loft gets absolutely soaking, as if someone has sprayed a hose up there.
It is definitely a condensation problem - turn the boiler off for a few days and it all drys up.

My theory is that as the trvs are satisfied the amount of water circulating is reduced and the water is overheated by the boiler until the room stat is satisfied.

1.Is this possible/probable?

2.Would an addition of a an auto bypass (bypassing the 3 port valve) help?
The hall rad has no trv and both valves are fully open. Is this not
sufficient to give enough flow rate to stop the boiler overheating?

3.Could the boiler stat be faulty? - how can i tell?

4.If the boiler stat is faulty, I replace it, then, is it acceptable for the system to utilise the boiler stat when it gets to the nearly satisfied condition of the room stat?

5.What temp should the water be in the F&E tank?

Thanks DKBB

 

[jobloggs]

a lot of posts on this.

Hot water is pumping up your vent pipe and over into your F&E tank.

Usual problem is due to siting of vent pipe which should branch off the flow from the boiler before it reaches the pump.

Problem is probably due to the CH loop being closed by zone valve or reduced by closed TRVs and all flow going to the Hot water cylinder's internal coil. Your vent may be branched off just before the coil and the feed branched in just after the coil. Seems to have been common practice in days before control valves.

You could try:

Reducing pump speed.

Raising the level of the bend over on the vent pipe higher above the level of water in F&E tank.

Adjusting water level in F&E tank to about one third full when cold.

Connect the flow and return pipework to the boiler downstream of the pump (ie on flow side) incorporating an automatic bypass valve in this link.

Resite vent & flow pipes to between boiler and pump. Big job depending where pump and controls are relative to boiler and HW cylinder.

 

[dkbb]

Well, it has an air seperator fitted. Looks to me like a copper Pegler one. The F&E exp feeds in at bottom connection, F&E vent pipe connected to top connection, flow from the boiler is connected to lower side connection and the feed to the pump is connected to the upper side connection.
From the pump it then goes directly to the 3 port valve which then splits the flow to either HW or CH circuit.

So the vent and flow pipes are in the flow pipe before the pump.

The return from the cylinder joins the return from the rads and then back to the boiler.

I am suprised if it is pumping up the vent pipe as the cold level in the F&E tank is not higher than when installed.

Thanks for prompt response
DKBB

 

[jobloggs]

you wrote

"Well, it has an air seperator fitted. Looks to me like a copper Pegler one. The F&E exp feeds in at bottom connection, F&E vent pipe connected to top connection, flow from the boiler is connected to lower side connection and the feed to the pump is connected to the upper side connection."

This is very confusing. Are you talking about vent and feed connections to indirect coil in HW cyl or to boiler?

Is pump and 3 way valve close to boiler or in hotpress?

 

[dkbb]

Sorry if I wasn't clear.

The Hw/cyl, pump, air seperator and 3 port valve are all in the airing cupboard. Boiler is situated on wall in the garage approx 5-6m pipe run away.

There is only one vent pipe and one feed/exp pipe on the primary circuit.
These are connected as per the previous post - to the air seperator, between the boiler and the pump.

I'm not sure what hotpress means.

DKBB

 

[JohnD]

.

I'm not sure what hotpress means.

DKBB

Scots for "Airing Cupboard"

 

[dkbb]

Does it matter where I position the bypass valve between the boiler flow and return?

I was thinking to connect a honeywell du145 directly after the pump on the flow and then link it to the return from the HW coil - very close to hw cyl

If I do this all the extra pipework is in the airing cupboard and it is an easy job. All the pipework would be in 22mm.

If there are lots of posts on condensation in lofts - I cant find them....

Thanks
DKBB

 

[JohnD]

also search on blocked f&e