Water hammer into heating system with no by-pass

[Sofita]

We have a sealed system with no by-pass balancing valve, but with 3 port valve(Drayton MA1), pls see scheme. Boiler - Potterton Suprima 40HE
There is three problem :
1.When Central heating(CH) mode finished and boiler stoped, 3 port valve Drayton doesn't come back automatically into deafult mode(its lever-indicator left in right position (CH mode)). Is it OK? In the valve's manual it's stated that 3 post valve should come back into default mode under the spring's influence. Our walve switches into default mode when boiler starts HW mode only.

2.Water hammer appeares every time when the boiler starts HW mode and previous mode was CH. Thus, Water hummer appeares when 3 port valve switch from CH into HW. Engineer said that by-pass valve must be installed, otherwise insurance copmany probably refuse to fix any problem with pump. BUT boiler's manual says that by-pass balancing valve is not necessary since one circuit is always open.

3. After boiler stops HW mode , 2 port valve Honeywell closes, but Pump is still working duirng 3-4 min and water doesn't cicrulate into the closed system and doesn't cool down the the boiler heat exchanger.

By-pass balancing definetily solves this issue, but we have no room for its installation and a lot of pipes replacement needs to be done.

The main question: does it make sence to remove 2 port valve and let water goes through cylinder after the HW stops?

Many thanks,

 

[ShaunCorbs]

Your best bet would be converte the system to an s plan setup (2 x 2 ports as you need a 2 port on the cylinder to stop it overheating and the water getting too hot)

And install a bypass valve at the same time

 

[Sofita]

ShaunCorbs, thanks for reply!
Is S plan much better than Y and it make sense to make extrawork? Could you please assess the apprximate cost of such replacement?

What make you think that cylinder overheat? If water become too hot I just turndown thermostat.

 

[ShaunCorbs]

Your best be would be ask a few local heating engys to give a price for the works

And if you remove the 2 port valve there's nothing to stop it still heating (2 port valve is there for a reason and connected to the cylinder stat)

 

[doitmyself]

Make and model no of your hot water cylinder, please.

 

[Sofita]

Make and model no of your hot water cylinder, please.

CenterStore, 150 litres, model - not sure, please see my photo

 

[ShaunCorbs]

Make and model no of your hot water cylinder, please.

it will be an unvented cylinder

 

[townfanjon]

S-plan always better , easier to diagnose any problems.

 

[Chalked]

You definitely need a bypass. You have a three port and a two port motorised valve. Therefore, when not water is satisfied, it shuts down and then your heating gets up to temp and reverts to hot water. Normally this would be ok, but as you have an extra zone valve on the cylinder ( which is correct) this is shut, so boiler has nowhere to circulate. An auto bypass fitted in the correct position in the system will correct this.
An "s" plan is a better way, but will still require a bypass.
Hope this clarifies.

 

[Sofita]

Chalked, your explanation is very clear. By-pass is really good decision and would definitely solve the problem.

Just let me explain what caused my question. There is a schema and information made by boiler's manufacture which states next:

If a three port valve is used as shown in Fig. 3 a by-pass is not
necessary since one circuit is always open.

And schema with 3 port valve and 2 port valve which is considered to be optinal:

Thus, according the manufacturer 2 port valves are optional and
by-pass is not necessary as one circuit is always open.

Secondly, we have no room for instaling by-pass and have to cut a lot of pipes and replace all vent what would by a really expensive. That's why I am seeking professional advice whether alternative solution is possible bearing in mind the manufacturer's instruction.

 

[ShaunCorbs]

Convert to s plan and stick a bypass in

Plenty of room there

 

[doitmyself]

it will be an unvented cylinder

I guessed that; just checking I was right.

OP:

The two-port valve connected to the cylinder is part of the safety system for the unvented hot water cylinder and must not be removed.

The mid position valve will stay in the heating only position when the call for heat ends. This is a quirk of the mid-position valve. As you have found, calling for HW resets the valve, as will turning the power off and on.

Removing the mid-position valve and putting a 2-port on the CH branch would be the best solution - you would need an auto-bypass after the pump.

 

[Sofita]

Doitmyself,
Thank you so much. I am really grateful everyone for you replies. In any case, I have to fix this issue and install by-pass. I am thinking about migration to S-plan because the work would be arranged anyway.

It is strange for me why this by-pass wasn't installed initially. Are there any regulations or rules which prescribe to install by-pass or it is optional component for such installation like mine?

 

[Chalked]

It initially would have had a three port. Then someone swapped the original cylinder for a pressurised one. This needs a positive off motorised valve as a fail safe to stop the cylinder being overheated. So an extra two port was fitted. At that point a differential bypass should have been fitted.

 

[Sofita]

Chalked, Yep, your are Nostradamus! It was really like you said. Cylinder was swapped by former owners. Small cylinder was likely replaced with a bigger one and moved from upstairs to the loft. Thus, missing by-pass is the fail of engineer who swapped the cylinder. It is very strange why Gas-Safe certified engineer missed such critical component.

 

[Sofita]

We have finally installed bypass and it wasn't such difficult as it seemed before. Just wish to share it, hope it will be useful for someone.

 

[ShaunCorbs]

thank you for an update and glad you sorted it and top job